The first thing I would do is crack open the repair manual, get the compression psi range, and rent a compression tester. If it's in the normal range don't worry about it. If it's already off the bike, just have it rehoned and replated. It almost sounds like your getting some sand sucked in the intake somewhere. If you are, The piston ring will thinner on the intake side when removed. Next time when you clean your air filter, take some grease and smear it around the lip of the filter to seal it to the airbox.