hello i have a 08 4x4, when i start my truck about 2-5seconds later a hear a bad almost grinding for around 2 seconds, im not really sure where it is coming from, sounds like the front or right under the cab, this only happens after my truck as not been turned off for a longer period of time, usually happens in the morning, then is fine after that till the next day.

 

My 07 did this since new, I'm almost positive it's the ac compressor. Don't know why it makes such an awful sound though. And yeah it only happens when my truck hasn't been driven for a while. Try this.. after your truck has been sitting for a while, start it with the defrost selector **** thing in the off position. See if it makes the noise. Then turn it to defrost (or ac, or feet/face) it'll probably make the noise when the compressor kicks on.

 

oh yeah that probably will be it, cause it started making it when it got hot out.....