hi everyone, i hope someone can help me with this rattle thats coming from under my truck..
its a 90 4runner v6 automatic with a 4" lift. its hella weird when drive in 2wd i get this loud rattle and it sounds like its coming from somewhere in the front or the transfer case. when im driving and i drop it into 4wd hi the rattling almost goes away, then i put it back in 2wd and its loud again. it sounds kinda like a bearing i think.. any help!!! thanks !!!!!!!!!!!!

 

I think your problem could very well be your front CV joints. Being that when you are in 4WD the load is coming from the transfer case, but when it is in 2WD the load is coming from the wheel and more or less free spinning. I woudl check those out, but they usually have more of a grinding sound then an actual rattle. Rattles usually come from a lose piece of metal like something along the exhaust.

 

I just had a noise like the one you described (fixed it tonight) and in my case it was the heat shield on the driver side that was loose and was knocking against my brake line. It was making this metal to metal noise almost every time i hit a bump, and was loud in the cab. Hope you find the problem