Under acceleration I have a rattling noise coming from somewhere under my car and the pitch of the rattle varies (sometimes its louder than others). Once the cruise control is set the noise goes away or more less can still be heard slightly but once you give it gas it's back.

It does not make this at idle.

I originally thought the exhaust was loose but it has to play to it.

Any ideas what it might be.

 

The last time I had a similar problem it was my exhaust hitting the body near the spare tire location...basically right under the cargo area. The rubber part on the rear-most exhaust hanger had shifted when I drug my exhaust coming off a rock ledge. I had to rotate the rubber part and tweak that exhaust hanger a bit with a pry-bar to get some clearance between the pipe and the body to get rid of my noise.

 

Might be a busted cat.

:wabbit2:

 

definitely... catalytic converter issue... or maybe the vibration dampener in front of the muffler is missing?? (my 4 runner made that same noise after I changed out the exhaust and didn't put the vibration dampener back on...)

 

Can you get someone to fluctuate the gas pedal while you get underneath the truck? maybe someone can get the vibration to occur while you're under there. then you can poke at some parts with a screwdriver and see if you can isolate the sound. i usually check for the heat shields at the cat and manifold first.

 

Yeah, I've had to replace several heat shield bolts (I have two cats). They just disappear.

 

That's what I originally thought when I did the same thing in the San Rafell Swell but I had that all fixed up a few months ago but the problem didn't go away.

It doesn't do it at idle; you can hit the gas all you want but it doesn't do it. It's only when moving.

 

Video, hopefully, you can hear the rattle

http://www.youtube.com/watch?v=hX8-AAvpGc4

 

If it's only while moving would bet it's a slightly bent or twisted somewhere exhaust.