Hi, I've got an MB210 that after a while of playing has a constant mechanical rattle/buzz coming from just under the input jacks. Its not coming though the speakers and to me sounds like a cooling fan with some kind of mechanical interference. Do these units have fans on thermal switches? If I turn the unit off for a minute it does not restart when I turn it back on and only starts after 20 mins of medium volume playing. I saw posts about other rattles when playing certain notes etc. It it fine except for my fear something is being worn down in there. I guess I should open it up but it was a "used" unit from MF and its still under the 45 day satisfaction "warranty". I would hate to return it if its just a wire that's got into the path of the fan blades or something simple like that. Thanks, Mike.