I have a 2008 Silverado LT 1500 cab and a half with the 5.3 flex fuel. It has 114,000 miles on it. For the last year or so when I go up a hill and floor it I would hear a clicking, chattering, ticking maybe knocking noise (I'm not sure how to describe it) from the engine. Gradually over time, I've started to hear the noise at a lower and lower rpm and now it's at the point to where it does it at a very low rpm like 2,000 or 3,000. I have tried seafoam in the gas tank and I changed the spark plugs 2 days ago. I use oil additives when I change the oil and I take very good care of her except for running her hard on occasion! What could the problem be?

 

Try replacing the plug wires

 

I replaced the plug wires also. It didn't change anything.