My gas cap has been driving me nuts lately. The metal covering part of the key cylinder on my gas cap rattles at certain RPMs. I have tried to spray some white lithium grease in there to try and quite it, but no dice. The only way I can get it to stop is to put my finger on it while I'm riding. I don't want to replace the cap as it is keyed the same as my ignition and helmet lock. Any ideas?