I bought my 2001 Blazer Lt with 40,000k about six years ago. It's always had this weird rattle which seems to me to be and engine issue because it only happens when accelerating(no performance issues). Doesn't matter if the acceleration is fast or slow. It sounds like its comming from the the heater vents. I have read a few post stating it could be some loose clips in the venting system, but since it only happens when accelerating it doesn't make sense. I have already checked the pcv valve and that is working fine. Another post mentioned something about 99-01 blazers having some sort of air valves, which are metal covered by rubber boots. Not sure what that is, if anything. Any ideas would be greatly appreciated, as I am pulling my hair out in frustration!

Thanks,
Jason

 

OK this is just a guess but a easy check get under your vehicle and check your exhaust heat shields. Just a quick check you can do in a few minutes.

 

^DITTO^ also check muffler clearance to the frame and hit the cat with your hand to see if some of the honeycomb broke off in the cat.

 

Also, a far fetched idea that could cause the rattle is a bad u joint on the rear drive shaft...that did it for me

 

never heard of that one before. what did the rattle sound like? just for future refrence.

 

it wasn't necessarily a rattle but it sure as hell caused alot of rattles, but it happened during acceleration, and not just normal coasting...i guess his could just be a u joint beginning to go bad?

 

Thanks for the ideas guys, checked out the cat and the exhaust and everything looks snug. Looks to me like plenty of clearence. The rattle is really hard to explain, it does sound like a heat shield or broken honeycomb in the cat. Not to long ago I bought a new muffler and all the pipe leaving it. The cat is actually the same one that was on when I bought the truck. My question is would it sound like its comming from the dash vents??? Really stange, mild boggling! I also recently noticed a gas smell when I get out of the truck, could it be a spark knock??? I've never heard one before.

 

I do have the same issue with my 99 Blazer.
Today I checked the pcv valve, the rattling is for sure comes from the pcv valve.
If I unplug the valve the rattling stopps.
Is the rattling normal?

 

Check to see if the PCV valve vacuum line is resting against the cruise and/or throttle cable. There actually is a TSB (technical service bulletin) about this very condition.

 

Thanks for all the ideas, it turns out that my cruise control cable was resting on my pcv line. Just didn't have any ties to tie it off. Gonna get some tomorrow!

Thanks so much,

Jason