Creaking from rear

[ChristopherDB]

When I'm at a stoplight and accelerate I hear a brief creaking sound when the suspension squats in the back. When I come to a hard top I also hear the creaking when the truck fully stops and the suspension levels out.

 

It just started happing this week and coincidentally I had the dealer install the GM performance exhaust. Could this be the exhaust rocking on the rubber hangers? Of so, are they supposed to be greased?

 

[ChristopherDB]

Creaking went away after a 50 mile trip on the highway at 80+mph.

 

I'm glad it's gone. Hope it doesn't come back. Can putting the truck up on a lift for a couple hours cause this creaking sound? The exhaust was installed 3 days ago.