There was a *strange* noise coming from the area of the right-side valve cover on my '81 R100RT after a ride this afternoon. It sounded like an air leak (I thought I had picked up a nail or something at first.) Is the crankcase pressurized? I quickly removed the dipstick - no change. Head gasket leaking (this was only the 2nd ride after changing pushrod tube seals)? I removed the spark plug - no change. The noise slowly died away and I never determined the source. I started the engine a couple of times but it never recurred. Advice, hints, theories, etc. appreciated! I've never heard a noise like this before.