Thump under front end !!!

[Harley05]

I was wondering if anyone has heard a thump and felt it on the floorboard after initial startup in the morning. The dealer told me it was the doors inside the ductwork for the heat and defrost and when it sits and looses vacume it will slam when vacuum comes back on startup. They told me it is only on a defrost setting and i found that it does not matter where it is set. If someone could let me know if they mabye found out how to fix it or if the know of another reason why it does it i would appreciate it thanks

[03f3507.3]

Originally Posted by Harley05

I was wondering if anyone has heard a thump and felt it on the floorboard after initial startup in the morning. The dealer told me it was the doors inside the ductwork for the heat and defrost and when it sits and looses vacume it will slam when vacuum comes back on startup. They told me it is only on a defrost setting and i found that it does not matter where it is set. If someone could let me know if they mabye found out how to fix it or if the know of another reason why it does it i would appreciate it thanks

I get that too and have always wondered wth it is?!

[sea71]

Ive heard it before in my truck, but when i would hear it, I would look and had started up with something(AC, Heater) on. I dont hear it if the control is OFF.

[strokermann]

i also get the same thing. ik read this post yesterday and when i started my truck up this morning. i also heard it but it came from the like the middle of the cab. and it h appen when i turned on the heater. maybe someone knows what it might be. but it seems it only happens when the truck has sat for more then a few hours and has had time to cool off. i am sure someone will chime in

[purduefarmboy460]

There is a post floatin around here somewhere that discusses this very sound, and yes, it is depicted as the duct work or a flap somwhere in the air system moving when it is cold.

I'm not sure where the post is right off hand.

[Harley05]

I think the reason that it wont do it with the select switch off is because all of the functions are run by vaccume. I also remember from somewhere about the gaskets on the flap doors being made poorly causing exess noise

[mschn99]

It is the heater blend door bangins shut when it gets vacume after the vacume has had a while to bleed down. It only happens in certain positions because the blend door is only in the open position under certain switch positions. It is completely normall and nothing to worry bout

[Harley05]

thanks for the info
at least its nothing wrong just alittle anoying to hear sometimes

[CHenry]

yep, i have heard it too and just figured it was something like that.

[saca93]

I'm getting a loud noise from under the floor when i leave from a stop. you can feel it in your feet any toughts?