Rattle while idling?

Hey guys, I have a 1995 Chevy Silverado 1500 4x4. Good truck by the way. Anyways, lately when I start it and it is idling in my driveway as Im about to leave my house and what not, I start to hear a rattling that sounds like my tailpipe is loose or sumthing, even though its not. It still rattles when I apply the brake, but as soon as Im moving it stops rattling. Then once I stop again, (usually for a longer period of time), it starts to rattle again. My friend says it may be my catalatic converter or sumthing to that effect. Is he right? and if so, how much would a decent one be to buy without going top dollar for one. Thx guys.

The idler pulley or tensioner can also make a rattle at idle. One way to be sure, is to remove the belt and start the engine (DO NOT DRIVE, since you will not have power steering). If the rattle goes away, you need to look at the idler, tensioner, alt, ps pump, water pump, etc.

Also, since the water pump will not be turning with the belt off, do not do this too long or you will overheat.

//2000CAYukon

Could be a loose heat shield, or a heat shield touching the exhaust.