richmod

06 GT Auto, 110K miles

I am getting a loud rattle/chatter noise in first and second gear when initially accelerating from slow speed or stop. Seems to be coming from either front or center underside of car. Thing is it occurs with foot on gas AND also when I let off the gas. it is a mettalic sound - best I can describe is if a a chain was being dragged across a loose piece of metal. it's a loose metallic vibrating sound.

I had a similar sound occur from the rear under similar conditions (only on tip in, not on foot off gas) not too long ago. Turned out to be a loose exhaust clamp. So I went under the car yesterday and tightened every bolt that I could reach - didn't help.

Any ideas? Bases on the fact that is occur under load and no load, I don't think it is tranny/gear related. I also don't feel any vibration - it is just a noise, but loud. Could bad catalytic converter make this noise?
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Nuke

You're describing a sound similar to what I had at one time. Mine was predominant at about 1200 RPM IIRC when the engine was still cold but it went away as the exhaust system heated and expanded. Tighten the axleback and midpipe clamps about a 1/4 -1/2 turn. If that doesn't fix it, look for the TSB for the tranny separator plate.

So_Cali

Have you done any recent work to the exhaust recently? Definitely sounds like something's loose or something

Derf00

There is a Torque Converter Inspection plate at the bottom of the tranny bell housing. Have you checked it to make sure the bolt that holds it is snug? Also, double check your heat shields above the rear cats. Make sure one isn't bent and touching something.

Could also be the heat shielding that is welded to the cats themselves. If a weld joint cracked or broke. Go through with a mallet and kind of tap around the cats gently. You'll hear it if you tap the broken area.

bones302

my vote is heat shields