Developed a new sound coming from somewhere in the car, VERY faint, very high frequency (imagine sound like a high pitched whine coming from a speaker, veeeeery faint), only happens when the TRANSMISSION (6MT) is under light load, releasing the accelerator pedal and the sound stops, give more throttle and the sound stops, hard to reproduce because there is only one sweet spot where I can make the sound.

The sound is so faint my wife can't even hear it, too quiet to get a sound clip recorded.

I suspected maybe an exhaust leak was developing or something allowing a harmonic noise into the cabin but didn't see anything out of the ordinary this morning when I was prying around on the pipes and inspecting gaskets, heat shrouds are solidly intact, no points of rattle. I suspect the sound is coming directly from the transmission but can't reproduce the sound with the vehicle on a lift. All I know is that it's driving me batshit crazy now that I'm aware of the sound lol.

Can't hear it with the windows down, can't hear it with the stereo on, SUUUUPER faint high frequency hum, anyone else experienced this? I wasn't planning on taking the transmission out until sometime this summer but if I can't get this noise figured out I might be doing a CD009 rebuild sooner than expected (slightly worn synchros not because of this noise).

 

Only thing that comes to mind is the throw-out bearing.