need help diagnosing noise

My 67 coupe has developed a noise under the hood that I'm trying to track down. This is a 331 stroker (6 months old) with T5 (installed "new"/rebuilt 18 months ago) and Centerforce clutch (6 months old). It's a chirping/whistling sound that has the following characteristics:

Always present when I crank the car, clutch in or out; as it warms it is sometimes present at idle, sometimes not. If it's not there at idle it immediately starts up again as I start off (let out clutch, apply gas). Under acceleration the noise turns into a constant fast chirp that sometimes varies depending upon if I'm on the throttle or off the throttle. Slowing for a stop, if I disengage the clutch and put it in neutral, sound will typically go away (clutch in or out). If while I'm still rolling in neutral I rev the engine, chirping/whistling sound comes back, then eases off as I let off the gas.

Initially thought it was the fan belt or alternator pulley bearing, because that seemed to me to be where the noise was coming from, but running the car without the belt has no effect on the noise. Others who have heard it say they think it's coming from the back of the engine. I'm now thinking throwout bearing or input shaft bearing but looking for opinions from others who may have experienced a similar problem?

Thanks.
 
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