I purchased my 01 coupe 6 speed with 114k miles a little over a month ago and about 2 weeks ago replaced the trans with one out of a 98 model with supposedly 60k miles because of a 4th gear grind, and did a trans and rear diff fluid change at that time. I think I believe this sound to have been there before the trans swap, but I never really payed attention to it until someone rode with me the other day and pointed it out because it isn't very loud and I figured it was probably normal like a throw out bearing noise.

Anyway, today while driving I did a little test and the sound seems to be coming from up under the shifter, or even a little further forward. But definitely does not sound like the sound is coming from behind the driver seat, though I know sounds can travel through the torque tube.

I notice it in all forward gears except 4th while accelerating or constant speed on the gas, goes away when not on the gas and also goes way when I push in the clutch. I will do some more testing to make sure it is completely gone in 4th. I have not tested reverse yet.

I used regular non synthetic valvoline atf in the trans because I read of the paper blocker rings that could be in the 98 trans, and used royal purple synthetic diff fluid in the rear diff that already had the friction modifier in it, should I add more to it?

I hope to take a video of the sound soon so you guys will know exactly what I am talking about. Everything works fine, the sound is just kind of annoying now that I know it is there and think about it, and worries me that it seems to go away in 4th knowing I just did all that work to replace the tranny. Is this something serious that needs attention or could I just let it ride and deal with the sound as long as nothing is going to fail? I hope to do an off road x pipe soon so maybe that will tune out the buzzing noise and ill no longer notice it