Boy that rear cam plug would have to be really F'ed up to cause a cam to be tight. Ive done it, and it sucks, but it didnt make that noise, it just made smoke come from the back of the engine where it was rubbing, then an oil leak from it spinning and falling out. BAD DAY by the way.

I hope ya find it, and hope its just not the headers/exhaust. My harley used to make some offley wierd noises from the exhaust, ended up being a bad header gasket is all.