i have an 02 silverado 5.3 with 79k miles i had the cats replaced at 65k but recently under hard acceleration my truck makes a kinda rattling noise and it sounds like its coming from under the truck or in the engine compartment i have done all the top end flushes i can do so i highly doubt its the valves rattling

 

Forgive the question,but are you sure you aren't having a Detonation(knock and ping) issue? I had a bad one on my 2002 5.3 Z71, that lasted 2months. It started that I couldn't BOOT the thing or it would sound like machine gun fire above 3500 RPM,then got worse, happening at lower RPM and lighter throttle over time. It was at 2 different Chevy Dealers(No codes for first 2-3K miles) and had wiped a set of converters(covered under emmisions warranty,thank god-$850). The dealers both did high pressure injector cleanings which helped both times for a couple of hundred miles,then it was back, they never did fix it. Out of desperation I let a "Old Timer" try his "old school" fix, it was fixed in one tank of gas and has been fine since 5months. He wouldn't tell me what he did till the other day. Get ready- he put 6 ounces of 100% pure Acetone in with a full tank of gas,according to him he's been using it on everything from chainsaws to heavy trucks for 40 plus years,never having had ANY problems. According to hi Acetone is or was a component of commercial gas anyway,just ahigher concentration of cleaner. I have to assume I have a lean condition under heavy load from crap in the fuel system before the fual rail where The High Pressure Injector cleaner system connects. I had already changed the fuel filter twice during that time and only the first one(god knows how old it was-only owned the truck 14 months) felt heavy from crap. I can't say for sure how safe or not this is,But solved my problem.

 

jpgoodnu,
thank you for all the advice i am going to definetly give it a shot im desperate also im a freak with noises and keep my truck clean and maintained. I also have had all the new products pushed pulled stuffed and scraped through that motor trying to get rid of it so i will give it a try. I thank you for help and im going to change the fuel filter then pour some acetone in there. sometimes the old school mechanics do it better they have the feel not the computer thanks again

 

make sure its not the cat rattling...but they sound really awful

 

Mine has a weird rattle too, at idle. Its not anything on the ouside of the exhaust, maybe the O2 sensors or something but I could never find out for sure. What do I look for? I comes from the cat-area of the exhaust.

 

I get under it wile trucks cold and shake the exhaust around to see if you can here anything. Or maybe try to hit the cat. to see if anything is lose.

 

I did that aq couple of time and it real hard to pin point. Even with the truck off. Its either the CAT or the o2 sensors (I think).

 

Unless the O2 sensor is real lose it shouldnt make any noise id say its your cats.

 

Has anyone considered maybe the heat shield, for the Cat? Just my .02 worth

 

Yep thats what id say it is I had the same prob on a differnt car. I just bent it so it didnt hit anything.