Porsche Repair: Rattle noise coming from heater boxes, nooks and crannies, heater boxes

Question
I have a 1990 911 C4 with 84000 miles. There is a rattling noise that seems to be coming from the engine compartment heater boxes that connect to the engine manifolds via orange flexible duct. The noise is a slight rattle when engine is running but can also be heard when you shake the car such as slamming the door. Is ther a cable adjustment for the flappers inside or some other kind of fix? The boxes look like they will be a little hard to get to with engine and exhaust in place but possible?

Answer
Hi Michael,

I'm sorry but I'll admit I've never had the pleasure of sticking my nose into other people's engine compartments to see what you are seeing.  You've certainly desribed the problem clerarly and your diagnosis seems perfect.  I've looked at my reference manual but even there I don't have anything to look at as current as your beauty.

If it were mine I'd poke and prod a bit more.  You probably do have an air contol flap inside the hose...or at the collector at one end or the other.  It seems odd there wouldn't be any outwardly visible evidence its there, for example, the end of a pivot rod protruding through the housing.  I'd take a tiny mirror and survey all the undersides and nooks and crannies to see if there is anything on the outside that looks like it would connect to a flap, and then it could be "adjusted" to silence your rattle.

Without the benefit of being there and peering down at your engine with you, I'm a bit helpless.  Sorry I couldn't be of any more assistance.

Dave