2007 GXP - Strange knocking noise to stump the best mechanic

[MikeJenkins]

2007 GXP, with new replaced engine and transmission, thanks to the 100K mile warranty.

Question:
I get a strange knocking noise when driving straight, no turning, when I get about 35 mph or faster. The knocking noise is annoying and sounds like somthing underneath the drivers feet slightly to the middle.

Acceleration and braking has no affect on the the noise. When going up or down a steep hill the sound has more knocking. It sounds like a loose bolt in the exhaust type of sound. Sometimes the sound goes away but will come back.

I have crawled under the car and used metal heat resistant tape to secure the exhaust sensor wire connectors but that was not it.

I took it to a mechannic shop and they couldn't figure it out.

Any ideas?

Chris

[Pontiacfanatic]

my 07 gxp makes a very vague and almost unaudible knock while at idle, and even less audible while driving. Im gonna swing it by a GM mechanic tomorrow or later this week. Maybe we will have something in common, so ill relay the info.

[MikeJenkins]

Awsome man! Hope you can figure out what the noise is in yours. Preciate it.

[Dan GXP Guelig]

Sounds like the media in the catalitic converter has broken loose and is rattling around in there. My buddies GMC truck with the 5.3 in it just did that to him, a little over 100K on the ODO. Just a thought.

[DoubleASE79]

Braking and Acceleration has no effect on the noise so it's not engine RPM related. It's vehicle speed related so related to something spinning at tire speed. If I'm correct, the noise should speed up the faster you go. Inner CV joint?

[MikeJenkins]

I found it is definatly something with the exaust. I havn't fixed it yet, but the other day it was missing a rubber tie rod or something in the middle of the exaust that was supposed to be holding it down. I replaced both on each side and the noice almost completely went away. It still does it now just around speeds of 50 or greater. Even then its not nearly as bad as before. I'm going to upgrade my exaust soon so hopefully that will stop whatever it is. I'll check out the CV joint as well just in case. It probly is something related to what Dan is saying.

Thanks for the help guys

[DoubleASE79]

Love trying to diagnose over the internet.

[blueguy]

Love trying to diagnose over the internet.

X2...it blows...ha.

I was going to say axles or hub assembly...those things are quite possibly the most annoying noises to me next to squealing belts and/or header leaks.

[IR II IP IDEATH]

Ha, I seen this thread and didnt even know it was you. Thats funny.