Starting to sound more like the chain, then, IMO.
If the chain were kinked really bad, I would actually take it off (remove front sprocket and rear wheel) and soak the heck out of it in some kerosene. Clean it really good, but leave it soaking for a day or two even. After that, soak it in a tub of lubricant for a good while, working the chain a bit as well to get the lube deep into the o-rings.
How old is the chain? Might also be worth just replacing it if it's that bad (if it does end up being the chain, that is).
What about rear wheel bearings? Does it get worse when leaned in corners?
2009 Aprilia Tuono - Ginger
2001 XR650R BRP (Big Red Pig)
2006 Honda 599 - Ex wrecked it :-D
2007 Honda CB900F (sold)
2006 Honda VTX 1300C (sold)