I have a 2004 Chevy Suburban 1500. It is a 2WD. The past year or so I only drive it every few days and have noticed that after it sits for a couple of days on start up it makes a horrible crunching noise. It sounds like two pieces of metal have locked together and are being forced apart. I took it to my local Chevy dealer/autoshop and they had no clue, nor could they get it to replicate the sound. This occurs during all seasons so I know it is not related to the weather. I have figured out that if I just go out and crank it every day it will not make that noise. Sometimes I forget or get busy though and it ends up sitting. It is kindof scary sometimes because it is so loud. Anybody got any ideas?

 

Welcome to the forum...
Could be the AC compressor slugging, might try removing the AC belt and try your starting routine and see if it goes away...

 

Does the sound change with the speed of the engine?
Does the sound change with the speed of the truck?

The A/C tensioner pulley is a common problem, too.