I understand all of this and the other parts of the reply about the pads, but (there is always a but)....

it is just that I find it very hard to believe the noise coming from steel (rusted or not) anywhere where the moving rotor and notch may touch, through many many revolutions when the brake is on , do not leave a score mark of some type. I will look again, this time with a proverbial "fine toothed comb."

New SS braid covered hoses 2 yrs old.

Let off the pedal and the noise stops immediately,  therefore fluid is returning

Hank,
are you thinking that nothing can go wrong with a caliper rebuild 2 years down the road?  Really?

Also if they're slow, I'd investigate a collapsed rubber brake hose not returning the fluid to the m/c.

No, you've still got it backwards. I'm talking about where the brake pads never touch.
Steel on steel would only make a bright mark if it was in constant, heavy pressure. When the disk/hub assembly deforms under uneven brake pressure (or cornering forces) and the disk rubs somewhere, it is barely touching and in maybe 2 or 3 spots at most. The metal and rust are too hard to be easily abraded. There is not enough pressure to make a noticeable mark and the mark would more likely be on the part being touched by the rotor - in your case probably the notch of the caliper. 

In contrast, a brake pad is intentionally soft and contains abrasives to maximize grip. The pad is intended to wear to continuously expose fresh abrasive material (which is also why they don't work well when glazed). The abrasive material cuts into the disk face for grip and ends up polishing and wearing the swept surface. If you look closely at the pad contact on the disk, it only touches on the clean part. The only time a pad would touch the unswept area is when the friction material is worn almost completely away to nothing and the steel pad baking plate would get close enough to the disk to touch.

The only time you might consider chamfering a pad is to try and remedy pad chatter, and you would do it only on its leading edge. Chamfering the sides would only reduce pad contact surface and brake efficiency.

Seems unlikely  - SS pistons in professionally rebuilt calipers placed 2 yrs ago.

pull the calipers, get kits and rebuild them. You could use your old pistons, but I think that the plating is pitted and that's what's causing your problem. Stuck piston. Get stainless pistons and the proper rubbers.

Dan, surely you meant
When the edge of a brake pad rubs on something..........

I can see perhaps something relatively soft like a pad not leave much trace, but steel on steel should leave a bright mark, pressure or not. 

I suppose I could do a test by chamfering the pads a slight amount and see if that avoids rubbing against the edge of the theoretically noisy unswept rusty rotor area.

When the edge of a brake disk rubs on something, there isn't enough pressure to grind down the unswept, rust-coated surfaces. Even with lots of noise, you won't see any marks, shiny or otherwise.

Understand.
no bright scrape marks on my rotor, either inner or outer face or outer end,  or dust shield

That's what I've been saying. On a car (not this one) with perfect brakes having floating calipers and a too-close dust shield, the disk CAN deflect enough to contact the dust shield and make a horrible noise only when braking. Unequal piston pressures from a fixed caliper as in this case will flex more.

Nope. Sorry to mislead. I did not stage that shot properly. The pads were just shoved in there for the photo, not lined up properly as they would be if shim and cotters were being placed.

Per my theory the "different forces" would be from unequal piston pressure or movement, but now I am not so sure about that.

My next step is simply to replace the pads with different grade and see if that stops the noise (that is only on one side). Again, rotors are new, smooth, and not scraping anywhere. 

This thread (and taking pictures of both sides) has helped me understand that BOTH sides have the rotor not centered in the caliper slot.  I don't know if the seemingly perfect wheel roller bearing condition has anything to do with the assembly and centering.

At the risk of being victimised by the parallax view, the pads seem to be positioned differently possibly resulting in different forces being apllied to outside and inside pads. Different forces may cause the rotor to flex a little.
See photo.

too much thinking

just got a new set of pads from Minimania in the mail today

the other pads I tried were two versions of Green Stuff. Maybe too hard and noisy on one side only becauue of Murphy

I am going to try these standard softer pads

not today - it just started to snow

another pic of R side ( opposite of noisy side)

this one pads : out and light pressure on pedal

pistons coming out more equally than they did on the L side where the noise is

after I did  this, I took it for a spin. You would think if my theory of unequal piston pressure on the L side inner piston was true, then it would not just be some sort of noisy harmonics on the rotor, but also unequal braking performance. Nope -  pretty straight as always, although if I lock it up,  the R front does lock up first .  This suggests R side (with both pistons moving equally) brakes better. However, the R side has ALWAYS  locked up first on this car, even before these calipers.

Furthermore, after a series of hard stops, both rotors read "over 500F"  on my handheld gadget. This is not a good clue, as the theorized one good piston L side could be 550, and the two good piston R side could be 700.

I am still working by exclusion and at this point feel the L caliper needs replacement I could be wrong.

edit: PS:I bought some SS washers and fender washers in case I find that I want to move the caliper over. Anyone do this? I imagine there needs to be enough surface area of the (two ) washers so the caliper will not be " wiggly." Anyone ever do this?

another pic of R side ( opposite of noise side)

pads out for another view

again, see rotor off center in slot but not scarping anywhere

outer piston look minimally pushed out compared to inner in this view 

okay - I looked a the other wheel

next picture R wheel (opposite side of noise problem) with pads still in -
shows same -
rotor is off-centered in the slot. On both sides, the rotor is located slightly medially rather than centered or laterally . This  means either it is just the way it is, or that both sides have some sort of equal wear (bearings?) so that the whole assembly has shifted equally. Again, no bearing noise, wheel turns by hand without any play or sensation of bearings loose or grinding. Had replaced roller bearings worn out in 2003. They currently seem perfect to me (without disassembly) and castle nut tight on both sides. Furthermore, there is no brake noise on this R side. Neither side has any bright scrape marks on any surface of the rotor or caliper. The hint of outer piston pushed out more ( on both sides ) must be related to this off center rotor as the pads have further to go.

Thanks guys

After I pushed the pistons out with the pedal (an 1/8 or so on the inner, a 1/4 on the outer) I had no trouble levering either back in. I was expecting the inner one to feel stiffer as I feel it is the problem.

Even though the caliper is not centered and the rotor looks off center in the slot, that still would not cause the inner piston to fail to move under pressure at a rate and distance equal to the outer piston. (with the pads out)

Plans

(A) Will examine other wheel and see how caliper pistons look as a comparison

(B) Will disassemble - either caliper replacement or bearings or both

44F at the moment and gray outside - maybe maybe I will do today

Appreciate all the advice . Will post followup eventually.  Harvey

Clamp off the flex line and go for a short drive around the neighborhood to see if the noise is still there, this will help you isolate the sound to a brake issue. Yes it will pull one way but just be prepared for it.
Looking at your caliper it is not centered to the disc so i am guessing something is worn creating this issue. I have had a few cars over the years with bearing issues that seemed fine with no noises until you took them apart then you wondered how they even stayed together.

The contact I was referring to is not with the pads, but with the slot in the caliper. The pads would be unaffected. Looking at your photos (and your subsequent comments), I'm beginning to follow your suspicion that the inner (left side in the photo ) piston does not seem to be moving under brake application. If this is the case, the piston with no balancing force from the stuck one would try to push the disk against the caliper slot. Even with perfect bearings and hub, the disk would flex a bit and/or the caliper might push itself outward. You could try putting in pale of the pads spacers approximately the thickness of a worn pad to see if the piston will travel significantly more. Then you might see what is restricting it. You should be able to lever the pistons back in. (If not, you've confirmed the problem!) Perhaps the accumulated tolerances of new pads and rotor have caused the piston to go too far in where it has become less effective - maybe a machining error in the bore or a rough spot or scar on the piston.

I can do that, but.....

there is no score mark on any part of the rotor - inner face, outer face, or edge.

the sound is not like metal screeching, more like hard plastic-like (the pad) riding on smooth surface (the rotor)

again, two pads tried -same noise . With and without backing plate goo - same noise

bearings: no play, no rumble, no bearing grinding when turning wheel by hand. New roller sets inner and outer in 2003 and only 1500 miles or so per year since then. Noise is ONLY on braking. In my experience, bearing noise would not be like that 

again - the fact staring me in the face is the photo of the inner piston not traveling as far when pedal pressure applied. Surely this must be the important clue. 

If it warms up today, I will look at the other wheel and do the same inspection, but I predict it will not look the same, the pistons there will move equally. Why would they not unless something was wrong? My theory is that asymmetrically applied force by the two pistons is somehow causing noise on the rotor, ie, only one side is doing the work of braking.