Expert: Grip Singh - 12/19/2006

Question
66.000 miles
right after intake manifold gasket's done.
cold weather top end knocking noise. ( starts up and warms up...5-10 min noise went away but next day will do same thing.  
( didn't use brown brush wheel, we uesed yellow rubber wheel for clean the intake manifold)
do you have any idea?

Answer
It has nothing to do with the intake manifold.

Unfortunately the 5.3L/5.7L/6.0L V8 series of Vortec engines suffer from piston slap in the cold. GM left too much clearance in the motors and the pistons slap around until the engine warms up.

Its not really harmful to the engine. Just annoying.