Squeak from the back end.

But hoping I could get a little help.I get a very loud squeak from what seems to be the back end of the bike under power. I don't notice it in first gear but 2nd and up I hear the squeak that is very loud. It is not a constant squeak but a jumpy one that seems to match the engine vibrations (as in it seems to squeak every time a cylinder fires) but only under power.I just put on new rubber on the back end last night and I left every guard off and it didn't change assuming that I have guards rubbing and squeaking but apparently not the case.Now what I find to be very interesting is that it is not always there. Case in point: Almost a month ago, I got caught in a pretty good rain storm. It didn't squeak again until I washed it. After I washed the bike, it never really went away until I ride for a while. Oh yeah, almost forgot to mention that the squeaking never really stays for a whole ride, just the start of it (10-20 minutes?)Is this a symptom of the wheel bearings going or do I have a problem with my belt drive? The bike is a 2003 XB9R and I know that there have been problems with the belt on some (not being strong enough) but from what I can tell, the belt looks imaculate for being 5 years old.Any ideas before I start throwing money at it until it gets figured out?,1. the belt will not squeak, so it's not that. 2. this is hard to figure out online.3. is it while riding constant or during normal/hard acceleration?,,,