Squeak When Shifting?

Hello,

I have the car listed above 2SS with the 6-speed manual.

Lately I have noticed it has a small squeak (maybe a half second or less, it isn’t a continuous squeak) when shifting from / to certain gears. It does have the auto rev match feature, and I’ve noticed this problem only occurs when the auto rev match is on (so I don’t think it has anything to do with the clutch / transmission). When I turn the auto rev match off, I don’t hear any squeak. Additionally, I have noticed it starts and continues after driving for a little bit (approx. 5-10 mins). The RPMs don’t seem to make a difference, whether I’m shifting at 2,000 or 4,000, etc.

I have mainly noticed it when:
Upshifting:
4 > 5 (Sometimes)
5 > 6

Downshifting:
6 > 5
5 > 4
4 > 3

I so far haven’t heard it:
Upshifting:
1 > 2
2 > 3
3 > 4

Downshifting:
3 > 2
2 > 1

Also, no sound when going into / out of reverse.