I have a 2006 GMC sierra, 4 door, 4.8l, 2 wheel drive with 104,000 miles. Just recently after a 270 mile trip it developed a "knock" or tick in the motor. It was an all-of-the sudden noise, just went outside, cranked it up and there she went. The knock follows the rpms, it speeds up with the motor, but doesn't get louder and actually seems to go away when the rpms are around the 3000 range. I've always changed the oil between 3000 to 4000 miles and the truck has great oil pressure and runs as smooth as ever. Pulley noise has been eliminated as I've taken the belt off and cranked it up and it was still there. I've never driven the truck hard and have always taken good care of it. Any suggestions would be awesome. Thanks!

http://www.pistonslap.com/

Moved to GMC

It is important to know if the knock or tick is coming from the top of the engine or the bottom. A ticking noise could be a bad lifter in the top end, and a knock could be piston slap or a bearing problem in the bottom. Use a mechanics stethoscope ($10 - $12 at a parts store) or a wood dowel to listen to various points on the engine to see if you can narrow down where the noise is coming from.

Ok, I've ran some seafoam through it twice and still same noise. We've determined that it is coming from the top of the engine just past the valve cover on the driver side. Any suggestions?

almost sounds like a loose TC or a collapsed lifter

Here are some links to videos of the engine. Check it out and see what you think. As for the collapsed lifter, that'* what I thought the whole time but I've had three mechanics tell me it wasn't but that really doesn't mean anything.

IDLE:

THROTTLING:

To me it sounds like something is rubbing. Have you removed the belt? If not, do that and start the engine. But don't run it for long, you will have no water moving. That will at least rule out pulleys, water pump and alt.

Yes I did remove the belt and run it, same noise.

It just sounds like something is rubbing and squeaking.