SOmetimes when starting up my Van, before engaging Transmission, I will hear a rumbling coming from what seems to be passenger middle to back side. The rumbling will go away after driving. This has been going on for 20,000 miles.
Occasional Rumbling heard from passenger side when starting up Van. on 1997 Ford Aerostar
Exhaust leak closes up after eng. warms up.
POSS EXH LEAK AT MANIFOLD OR HEAD PIPEOR CRACK IN MANIFOLD. PULL DOG HOSE AND LOOK FOR SPOT WITH BLACK CARBON BUILD UP AND THAT WILL BE YOUR LEAK