LTDScott said, "This weekend I plan to get under the car with a stethoscope to listen all over and determine the source, but I have to keep the car mobile so I can't start tearing it apart."
It might not be a good idea to keep driving it, if that's what you mean by "mobile".
Just speculating; maybe the slight change in sound when pushing the clutch indicates a thrust bearing issue?
Good luck. I hope it's not major.
'87, 105,000 mile stk short, SN89 Paxton 5 LBS, X303 Hds, E303, Cobra Int, 70 mm TB, 30# injrs, 1 5/8 full leng, no cats, 2 1/2 w/dumps, A5, 3.73, ET R's, Frnt Drag Eibach sprngs, Baseline Relocated upprs, HPM lwr arms, stk rear sprngs 1 coil cut, adj. struts shocks, 3150 w/dr. 1.60 11.39 118.