hey all. I've got a 2004 rx8 with 97k miles 6speed transmission.

got my clutch done with a full clutch kit in Jan 2022. The shop I got it done at did it pretty good job for incredibly cheap and fast. I had a full clutch kit: a ClutchMaxPRO Performance Stage 1 Clutch Kit: https://a.co/d/0GsPP7T

they did a trans fluid change as well and, save for a couple of unique, new noises that were pretty quiet at 3000rpm in any gear, I've had no problems for a while, then a month ago I noticed a slight whine with the clutch not pressed in while in neutral. with the clutch pushed in the noise would entirely go away and it wouldn't occur either while in gear, so I didn't think much of it since it wasn't all too loud and wasn't persistent every time.

recently I went on a pretty regular 100mi trip down from Bellingham WA to Lynnwood WA. drive wasn't really notable, until once I got back into Bellingham I noticed a very noticeable transmission whine while accelerating that was entirely novel. no problems with performance yet but my rx8 is straight piped with the OEM exhaust and it can make noise (really only with the foot down) and it's impossible for you to not hear it unless you are absolutely flooring it or blasting music windows up.

what do you guys think the problem is? I was just about to replace my diff fluid and serpentine belt and I doubt that's related; but should I put the spare 75w-90 oil I don't put in my diff into my transmission? I'm pretty concerned something major is about to break given the noise being so noticeable and so sudden.

 

Diff ans trans don't take the same fluid, so don't mix them. What fluid was used?