Alright. So around 2.5-3k rpm in 2nd and 3rd gear, a sweet spot hits and I get a bizarre squeak that increases with rpm. It's NOT consistent and does not occur all the time. When I clutch in, the noise goes away.
I've put the car up on jacks in the rear and tried to identify what the issue was. I was pretty sure that it was the half shaft and/or the U-joint, because I saw that the rubber in the U-joint was totally dried out (I shot WD-40 at it and the sqeak went away for about 2 minutes). I replaced the half shaft on the side that had the squeak, drove for about a quarter mile, and heard the squeak again.
I now have two theories. 1. Wheel bearings (not likely. I replaced both rear wheel bearings in the last year.) 2. Wheel bearing seal.
I have been meaning to put the car back up on jacks and take a look at it. Any ideas on what the squeak is?