Hello - When I start the engine it idles fine and sounds good however when I increase the RPM's to 1/4 of the way up it make a loud rapping sound. I don't really know how to describe it other then mmmmMMMM RAAAAAAAA then back to mmmmmmm after I let off the throttle. Its like you can hear something disengaging/turning off when the loud noise goes away (it stops abruptly). It does not do this initially but only after about 30 seconds of running (meaning i can rev it with no issues for first 30 seconds then it starts to make that sound while revving after 30 seconds). Is this a bearing, pump, other? Any thoughts or ideas would be greatly appreciated. Everything on this machine is stock.