My 1994 Chevy 1500 4x4 has a knocking noise right under the glove
compartment. It only makes the noise when you first turn the truck on
for about 30 seconds and then right when you turn the truck off for
about 30 seconds. We found where it is occurring and can push on some
plastic part hard enough that it stops while you hold it. I am not sure
what it is or why it is doing it. It just started one day when I
started my truck from picking up a pizza. If anyone could help me out,
I would be appreciative.

COULD BE THE HEATER FAN MOTOR, ITS LOCATED IN THAT AREA<IMG src=smileys/smiley2.gif border="0">

I have a 93 Suburban that does the same thing. Its a flapper valve. If you reach under there and feel you can feel it opening and closing. I do not know what causes it but would like to know. It is some kind of fresh air or recircualtion flapper.

I have a 93 Suburban and this just started happening to me 3 days ago. I can also press on the plastic part and stop the noise if I hold it long enough. I took the blower motor out and disconnected it and it still makes the noise so I know its not the blower motor like some mechanic told me it was.

Has anyone fixed this yet? Seems like it would be easy if you could just get to the part. I stuck my hand all up whwere the blower motor goes and cant feel any gears or anything. I feel the flap and can feel the knock but cannot tell what is making it knock and where exactly its coming from. Its the weirdest thing.

Buddy