[VegasDiesel]

After I start the car, about 5-10 seconds I get a big "Bang" from what sounds like the passenger side of the engine bay underside. Like someone took a rubber slegdehammer and cracked it a good one. Anyone else getting this?

 

[dikkstarr]

might be the ac comp kicking on, mines a loud knock too but not that loud.

 

[Joelzme]

Yea, I get the same muffled "thud" with the AC compressor kicking in too. Try turning it off and see if that fixes the problem. It almost sounds like there is some movable flap or door that is making a thud closed.

Joel

 

[VegasDiesel]

That's exactly what it sounds like. Thank god. I had no clue what that was. Now I have to pay attention to see that it doesn't do it when it's off cause I think it still does...

 

[hitecdan]

After I start the car, about 5-10 seconds I get a big "Bang" from what sounds like the passenger side of the engine bay underside. Like someone took a rubber slegdehammer and cracked it a good one. Anyone else getting this?

Well, if it's your "car", I have no clue what it is. If it's your diesel powered truck, it probably is the defrost/vent door moving from defrost to vent in the vent plenum. Turbo diesels engines do not produce an intake manifold vacuum like natural aspirated engines. Your truck has an electric vacuum pump and vacuum chamber to produce a vacuum to drive not only the defrost/heater vent door but also the front hubs on trucks equipped with shift on the fly 4 wheel drive. It takes some time for the vacuum chamber to pump down to a level that will drive the defrost/heater vent which is vacuum activated. If your vent control is on vent, and air is blowing out of the defroster vent, your system has a vacuum leak or the vacuum pump is dead since defrost is the default position.

 

[tattoocharlie]

vent door is correct