On my last few cruises in my FFR Roadster, this strange noise has developed.
It sounds like a low brake pad warning indicator, although it is more subtle, and no where near as irritating. It is also intermittent. Sometimes I can drive for a half hour or more, then it will suddenly start up. Other times if I come to a stop it will disappear, then start again later. It always disappears when I slow to less than 15-20mph.

The pitch and volume do not change if I step on the brake. It happens if I am coasting out of gear, foot off clutch, or in gear with clutch in. It does it regardless of what gear I am in, and doesn't vary, sound wise, regardless of the speed I am going. Revving the engine makes no difference, in gear or out.

I have the Ford 88 T-Bird turbo coupe 8.8" rear end, with the self adjusting rear disc brakes. 3.55 gears, professionally shortened drive shaft, with new u joints. The rear end was also torn down and rebuilt, all new bearings, crush sleeve, properly shimmed to specs, torqued and checked with a dial run out indicator, etc, etc.. I mention this as the sound seems to be coming from the rear of the car. Hard to say exactly, as the side pipes are loud.
The brake pads front and rear are barely worn, although they do spew a lot of dust. Part of the price for getting good stopping power.
I have jacked the car up, and given it a thorough visual inspection, nothing obvious, IE rub from e-brake cable, etc.
I checked my e-brake adjustment and the cable is slack enough to fully release the pads. Initially, I though there may have been some debris stuck between the pad and the rotor, so I pulled the wheel, (which loosens the rotor) wiggled the rotor, and tapped the caliper with hammer, hoping something may fall out. I may have to pull the caliper and pads and check further but the sound doesn't change one iota in either volume or pitch when on the brakes, or off, so I question this being an area of concern.

I have greased all my u-joints, and rear suspension, evn sprayed a little silicone lubricant up into the rear pinion seal area, as this was suggested as a possible culprit. I also heard of the rear tranny seal drying out at the yoke, so I smeared a tad of grease on the yoke near the seal.
Still no difference.

I don't know whether to just keep driving it and see if the sound disappears mysteriously as it appeared, or to start tearing things apart.

I was hoping that some of you may make suggestions as to where to start, or if you have had a similar issue, that you solved..
I have just less than 2500 miles on the roadster since completion

Thanks!

PS, why do this sites smilie's invade the left portion of the area I am posting to? I cant use the scroll bar either? Bit of a pain..