I am having a problem with my 2008 Prowler XT650. At idle it has a terrible rattling/knocking noise coming from the engine area. Sounds like there is something knocking or banging, as well as something rattling. When the engine is revved up, even just a little, the noise goes almost completely away. I have removed the drive side cover and it doesn't seem to be the belt or clutches. Any ideas where to look?