whenever i start my truck after a bit of sitting it makes an odd crackling noise right at startup like when you hear unpopped popcorn seeds rattling around in an electric popcorn maker. the loudness and duration of the noise depends on the temperature and longitivity since its been started last. if i start it again right after turning it off or within an hour of being started it wont make the noise if it does then its very faint. during warmer days its not as bad. but in winter, starting it up to go to work. if it helps the noise can be described as a bunch of ticking like a loose part flying around. my dad told me its the starter, my more knowledgeable cousin said it could be the AC pump. what are your ideas? has anyone else had the problem?

 

most likely broken exhaust studs on one side of the manifold

 

Sounds like your cats have gone bad and your hearing the screening rattling around

 

I think this is one of those things that you are just going to have to take it in for. The symptoms are just too vague.

Have you had someone else start it up while you peer under the hood to locate the source of the noise?

On another note, I had a similar problem. A small rock found its way in between the left rear cat and the heat shield. The RPM's during initial start-up, that first ~20-30 seconds, were just right to rattle that stone in there. But after it would kick down to a normal idle, it would stop. I pried open one edge of the heat shield and pulled that rock out of there and no more rattles!