That engine is twenty-some years old. You'd think there has got to be some play with the rings at this point. Certainly, head gasket leaks can make some noise and cause power loss. Valves, too, if not functioning properly, can mess with your mind. I'd say, do what you can and if all else fails, pull the engine and drop it off at the shop. Winter is a great time to get good service..........Don't wait 'til it throws a rod and you've got an UNrebuildable block!