Weird squealing when engine decelerates
 

I have a 2006 Z that I just changed the clutch, flywheel (lightweight), pressure plate, throw out bearing and pilot bushing on (all Excedy), and my first drive after cruising for a little bit I noticed that if I let off the gas between 3k and 2k rpm, I would get a squealing sound, sort of resembling a hamster stuck between some really old brake pads. It happens regardless of clutch engagement and gear (as well as neutral). If I don’t do anything and let the engine coast down then I’ll get the squealing noise.

I initially thought it could be that I installed the pilot bushing wrong (how would I even be able to do that) or the throw out bearing. However, I ruled both of these out because

A) In my mind, a pilot bushing issue would get louder with speed, and this sound goes away after 3k rpm. Also, it wouldn’t happen if the clutch was engaged since the bushing and input shaft would be spinning at the same speed

B) the throw out couldn’t be the issue because it happens regardless of whether the clutch is pushed in or not, and throw out issues usually happen with the clutch pedal pushed in.

So im really confused as to what the issue could be, I initially thought it was something to do with new parts needing to be broken in, but now with about 1500 miles on the new clutch it seems that is not the case. The noise hasn’t gotten louder or quieter in the time ive driven it, and it happens regardless of whether the engine is warm or cold.

I read around and couldnt find a match to my exact issue, but I saw a similar thread about something stuck on the VVT, but as far as I know I’ve never touched it and it only happened after I installed the new clutch. I also saw that it could be the lightweight flywheel but I don’t think the sound was similar to mine and the circumstances were different.

Any and all help is appreciated and I will provide more info if needed

It is probably the transmission input shaft bearing making the noise you describe. This noise is a problem with the CD009 transmission. I believe the CD00A transmission (upgrade of the CD009) fixes this (no noise).

The noise is "cosmetic" and does not result in damage or a problem (other than it is annoying).

Seems like a very likely culprit, except it happens with the clutch out too?

For sure... I see that is when the noise is worse.

The CD00A fixes this noise, but the noise is probably not enough to replace the CD009 for just that reason.

I thought about it more and more, and it can’t be the front trans bearing either, cause the car can be completely stationary and in gear (input shaft not moving) and it will still make the noise. There has to be something on the engine side making the noise, maybe the rear main seal? I neglected to change that but I’m not sure why that would come up after I put a new clutch in.

Loose fan belt?

Thats what I originally thought, but with the hood open you can’t hear anything from the front of the engine, it’s coming from the rear of the engine bay

Wonder if the crank has excessive end float which is affecting the clutch somehow? Easy enough to check at the front.

How would one go about checking such a thing?

It's a bit of a long shot, no, it's a very long shot. Warning, I have not tried this but get a lever behind the harmonic balancer and push gently, try and move the crank backwards and forwards. Any noticeable movement is too much.