A... Thud noise at idle?

[HighOn20s]

So the wife and I ran to the parts store tonight to get a new brake light and she sat in the truck to keep dry.. when I got back she said he heard a thud noise coming from the engine area so I let it idle and I heard it also.. It almost sounds like something it opening and closing.. .i could be sounding extremely rookie right now but what the hell is it?

[AlwaysStrokin']

I hear that too right after I start it up and run it for a bit. I would sure like to know what it is too. I'm stumped especially since it only happens every once in a while and some times more frequently than not. Seems like it only does it once to me after start up though.

[dieselkane]

Could just be the EGR valve cycling, or it could be the A/C compressor kicking on and off. The compressor also runs when the system is set to defrost.

[HighOn20s]

Originally Posted by dieselkane

Could just be the EGR valve cycling, or it could be the A/C compressor kicking on and off. The compressor also runs when the system is set to defrost.

That could make sence since the defrost was on.

[08stroker250]

It is the A/C compressor. Mine is ridiculously loud. Definitely not the EGR valve though.

[t.c.ben]

Yup I just noticed the same thing the other night, kind of like a thud coming from the passenger side foot well, only noticeable when the truck is on defrost and really low fan. Def seems to be the compressor or something to do with the HVAC and you can't hear it from outside the truck. Def freaked me out though

[powerhoghp]

Blend door possibly since it is heard in the cab with low environmental noise?

[HoleShot08]

^^What he said^^ If the heat or a/c control is not turned to high setting the door opens and closes to reg the temp. Its no biggie. My 99 did it for 10 years and the 08 does the same thing.
-Mike