There is a slight rattling sound coming from my 95 E300D when it is running at idle. The sound goes away when the gas is pressed. It appears to be coming from the engine bay (but i can hear it in the car) and only rattles when the car is up to operating temperature. My local indy thinks the intake line resonance flap is broken or the resonance shaft is worn. I took his diagnosis under advisement before I committed to the repair. He didn't quote me a number.

Does his diagnosis seem correct? What is the function of this flap?

As luck will have it, I planning to take the car on a 2000 mile road trip in a few days and I just don't have the time to have this repair made until I get back. If it is the flap, due I risk any engine damage if I operate the car without making the repair?