Meat grinder

i just noticed this the other day, after it sat for a while I would start the Riv, and it turns over fine, but i noticed a wierd noise, like a coffee can full of metal shavings being shaken up, at idle. when id hit the gas, the sound would disappear, and return as the RPM's dropped back down, after about 2 minutes it would be completely gone.

Anyone know what the deal with this is?

Probably the S/C coupler. Alot of people have this problem see the write up here-->http://www3.sympatico.ca/aepa/blowerinstall.html If that dosen't fix the problem look to the harmonic balancer.