GMC Repair: 2000gmc 3500hd 6.5diesel, drive shaft, necessary thanks

Question
Hi,My truck is a dually with auto. trans. When you drive you here like scraps of metal and smells like brakes. When it happened for the first time it sounded like something broke off and then was just spinning around. Since then at times it comes and goes. You here it by the cab. Not the motor and only when in movement. Any ideas.. Thanks.

Answer
If you are smelling brakes, it would be a good idea to pull the front wheels off and look at all the brake stuff.  Anything having to do with the wheels or brakes would be silent unless the truck is moving.  Also, if the sound is by the cab and definitely not out by the wheels, then you should look at the front drive shaft (you didn't say whether your truck was 4 wheel drive or not, but assuming it is).  The front drive shaft is motionless unless you are moving, so that's a possibility too.  Check those things and reply if necessary.  Thanks