happens mostly (almost exclusively) with the clutch out, while accelerating. sounds like its coming from the transmission itself but can't feel anything in the shifter or clutch pedal. clutch fluid was slightly low. at 60mph it goes from a rattle/tick/grind to a high-pitched reverb like a tuning fork, but only exactly at 60mph regardless of gear.

afaik the noise completely stops with the clutch fully depressed

not sure where to start really, just appeared today on a testdrive after replacing coils and plugs.

 

also tested: driving in a straight line about 35mph, wrenching the steering wheel left to right and keeping speed constant has no effect on the noise. not wheel bearing or suspension related. i believe it is related to the clutch as about halfway through the biting point the noise disappears while depressing the pedal

 

final test of the night: noise is related to vehicle speed, not RPM dependent. shouldn't be clutch or input shaft bearing. tailshaft?

 

if clutch wasn't effecting the sound i'd have already ordered an output shaft bearing. i'm stumped as to how the clutch prevents the sound but its also speed dependent and not RPM dependent?

 

doesn't happen with proshaft disconnected, only while in gear, not in neutral