My 99 Silverado has really bad valve chatter. I went to the beach and was low on gas so went to the gas station and put in like $15 enoughg to get home (cheaper gas near house 1.89 gallon on beach) as soon as I got on the road the valves started to rattle LOUD. any ideas 118,000 miles on it I know that chevys seem to have some chatter but my SES light is on (knock sensors) Any ideas?

 

Time for a top engine cleaning. Do a search here on top engine cleaner. Its a GM solvent that will remove carbon buildup in the chambers and PCV oil from the intake system. It will reduce detonation better afterwards. With 118K miles, you should really notice the difference afterwards.

 

Is it detonation knock, or valvetrain noise?

If it's valvetrain noise, something is definitely wrong. Broken spring, rocker loosing it's bearings, lifter colapse...

All of those would make a "single" tick/tap/knock noise though - not a harmony of 8-16 noises.

 

its defentily valve noise had it befor after about two tanks it went away my dad has a 01 6.0L and it has chatter even when it was new.