My gas cap use to squeal like crazy when the weather got hot. At times, I could barely open up the gas cap with all the suction it created. I took my overly complex gas cap apart and removed a little spring that pressed a plastic valve against air relief valve. I think it's there to prevent gas from coming out if the bike is tipped over, but I'm not sure. Anyways, venting has worked perfectly since, no squealing or excessive suction when opening up the cap. I figured, if the bike crashes or tips over, a small amount of gas on the pavement is going to be the least of my worries. Besides, there's a tip-over sensor that kills the engine, so fire is very unlikely. I got the idea from a forum; I wish I could find it...