'04 V-10 Upon start up, maybe 15-30 seconds later I get a thump sounds & feels like from the passenger side engine compartment, the other morning it was like a huge thump.

Will the vacuum pump do this?

I haven't put the tranny in gear, just idling. Everything runs fine, no lights on the dash, no increase in RPM, no squeaks, just a thump like something is engaging.

 

It is very likely a flapper doohickey in the heater box (As you can see I am using the technical term here). This is very common, my truck does it, and I don't believe it is a problem

 

My 02 does it occasionally too. First time it happened I thought someone had backed into me! And it does sound like a sticking door somewhere in the a/c-heater. Seems to be getting quieter with time though.

 

HVAC blend door...

they can make a startling amount of noise sometimes.

 

Thanks guys, now that it's mentioned I've only noticed it recently since I've been using the heat.

 

Don't feel bad, my dad had no idea what that sound was until I told him. And he has owned a V10 SD since 98'.

 

Mine does it, too. It's loud enough it startled Sand_Wife when she first heard it.

 

Not to be technical, but it is the recirc door that makes the noise, not the blend door which is electronic and physically unable to move quickly. If there is a vacuum leak in the a/c system, the recirc door will slowly move to the open position. When the truck is started, vacuum rapidly builds in the system and the door will slam shut again, making the noise. This just means you have a minor leak in the vacuum system, probably not worth spending time searching for.

 

This made me chuckle a bit. Does she know she is Sand_wife?

 

Ehhhh...no. She think's she's Sand_Goddess.

 

Nice! Goddess, dont they all!

 

Thank you for this explanation!

 

I also get this with my 03 CC V10. Mine sounds like someday is striking the firewall with a large hammer. Not only is it loud but I can feel it through the steering wheel, pedals and floor and it shakes anything I have lying on the dash. It doesn't do it every time I start the engine after its been sitting awhile, and I never change the selector from defrost/floor.