sometimes when first start truck up after a sec there will be a thunk kind of noise. just wondering what you guys might think it might be.

 

Does it do the same thing if you were to just turn the key to the on (not start) position?

 

not that ive noticed. was always after i started it up

 

HVAC blend door closing..

it can actualy make a hell of a noise some times..

 

ah alright thanks glad it isnt anything major. yeah it does sometimes sounds like a piston is going to fly threw the engine it seems like sometimes hate it lol. good to know that nothing big though

 

Yep mine does that intermittently too. Scares the bejeezus out of me most times, because it's sporadic, lol.

 

Just to be clear, is this the noise that is heard when you turn the key to the ON position, then hear the THUNK? I figured it was normal, but wasn't ever sure. I hear it everytime.

 

For me it's only occurred after the engine has started.

 

If I turn the key to ON, let it sit a second, I hear the noise, if I just go straight to START, I don't hear it because, I'm guessing, the sound of the engine masks it.

 

Hmm. I haven't ever experienced that, and I usually turn the key to the on position until all the idiot lights turn off before starting (too much time spent with diesel engines on heavy equipment). Then when it occurs, it'll sometimes make a loud thunk; sometimes it's not as loud, but still audible, within a few seconds after starting. Most times when it does this, I have the fan switch turned on. When I turn it in the off position, it usually doesn't thunk.