[SoCal LS-L]

Originally Posted by 92snowmachine

unfortunately you can't check the timing with a timing light because the ignition timing is computer controlled, and the data from the computer isn't really helpful unless you have a serious problem. if you take off the covers and the timing is off then you can adjust it by loosening the tensioner bolts, removing an idler pulley and having a helper turn the cam sprocket a notch with an open ended wrench while you slip the belt into the next notch (they are usually only out a notch or two). although if it has slipped you might want to go ahead and replace the belt and make sure all of your pulleys and the tensioner are ok.
can you hear the noise well from underneath the engine or transmission area? is sounds like one of your cylinders might not be firing all the time, try pulling off injector connectors one at a time and make sure that the rpms drop the same amount for each cylinder.

If you do this expect to remove some parts to take your tensioner out and recompress it. Basically a full timing belt job, since the middle cover has to be yanked to get to the tensioner and the belt would be loose ready to come out. Just letting ya know, check it first and then tell us what you find, we will go from there.

BTW 92Snowmachine, go Avalanche!!! Im gonna be moving back there in about a year, been an Avs fan since we stole them from Quebec.