Weird. Maybe a mechanic's stethascope (or a dowel rod, whatever is on hand!) would help find out exactly where the problem is? Stick it in yer ear against the bone, and the other end on the engine where you think the noise is coming from. Humming buzz maybe sounds like fuel pump, but its in the back...Aux water pump can go bad and make some noise, but can't imagine it being loud enough to hear in cockpit. Dunno why much of anything would make a sound after the engine is off.


cheers,
dan r.

ps. we might be having a gtg in SW florida (naples/ft myers area) in the next few weeks. drop me a line when you come through and we'll have a cold one if nothing else