This is a strange one and it's not unique to the '04s. My '01 Screw did the same thing. The first time I start the truck in the day, and after about 10-15 seconds of it running, I get a single "thump" that you can hear/feel in the floor of the truck.

I'm not worried about it because both rigs have done it and it's probably just something that is going on by design.

Any idea?

 

Mine does it too. '04 Regular cab 5.4L XLT

 

Yup... me too. I hear the mini sonic boom when I turn on my AC. If the AC is on when I start up, the noise happens when the unit kicks in shorly after I start up.

Experts... Is this normal???

 

I've heard it's normal. When the ac or defroster is on something about a vent opening. Some people heard it close back up after shutting off the truck.

I don't think it's a problem, and I also experience it. Must be a big vent...


Chan

 

my screw does it too 5.4 I was thinking flap sticks now @ then BUT it only does when I turn the heat on I thought it was normal

 

Mine does the same thing. I think it is just a vent opening or closing. It is not that loud or hard enough to feel, though.

 

Its just a vent opening in the A/C. No biggie.

 

Do you adjust any of your air controls after shutting off the truck? If so, then you are creating the noise yourself. If you feel some need to change the air settings when you park, then at least change them before shutting the truck off.

 

If it happens when you turn the A/C on (which also goes on when in any defrost mode) what's happening is called "slugging".

Under certain conditions it's normal, but still obnoxious. I believe the refrigerant gets heated up in the low pressure line when the vehicle is off. Then a bunch of cold+dense refrigerant comes and basically rams the stuff that has been heated up.