For some time now (like a year or more) I have been hearing what I believe to be a valve tap. Although it has not yet turned into a problem I am concerned that it may at some point. I have a 94 940 with a non-turbo 8 valve 4 cylinder. I'm running cheap gas (for obvious reasons) which may be contributing to this. Does anyone have any advice or information about this condition or how to verify that it is not going to errupt into a much bigger problem? Thanks!!

Your knock sensor should take care of engine knocking, so your tap may be due either to preignition from combustion deposits in one cylinder (try Techron to remove these), maladjusted valve tappet clearance, or worn valve hushers. See the 700/900 FAQ for information on the latter.