99 Envoy - Banging on the Highway

[appstech]

I would be eternally gratefull if someone could give me some direction on this. At 70 - 110 kms I have a very random banging noise comming from under the vehicle. I have tried shutting off the vehicle while at speed - noise still there, I have tried engaging 4x4 - noise still there. It sounds like something swinging around in the wind and banging on the bottom of the vehicle. It is on the right side right around the bottom of the passengers seat. It will happen every time I get to that speed. I have looked underneath and have found no obvious shields or exhaust loose. The banging almost sounds like firecrackers going off.

Absolutely any help would be majorly appreciated as my wife is going to kill me if I don't get this fixed.

[maxwedge]

Get it on a lift and look close around the driveshaft and exhaust system, tough to diagnose noises in this environment. Okay, this is not really the forum as this is the older Blazer/S10 type truck but somewhat the same advise. Look at the torsion bar mount at the trrans crossmember area also, and the trans mount.

[appstech]

It seems that the exhaust is making the banging. There appears to be a hangar bracket (just behind the Cat) missing. This bracket has been discontinued by GM. I think I will install an aftermarket one to help control the movement of the exhaust. All of the rubber hangars are dry and making some noise as well. I will have them lubed to help control noise. The banging noise will not happen in the rain. This leads me to believe that the rubber exhaust hangers are being lubed by the rain water. I will post more later on whether this fix works.

[appstech]

Originally Posted by appstech

It seems that the exhaust is making the banging. There appears to be a hangar bracket (just behind the Cat) missing. This bracket has been discontinued by GM. I think I will install an aftermarket one to help control the movement of the exhaust. All of the rubber hangars are dry and making some noise as well. I will have them lubed to help control noise. The banging noise will not happen in the rain. This leads me to believe that the rubber exhaust hangers are being lubed by the rain water. I will post more later on whether this fix works.

OK, Your not going to believe this. The banging noise was the roof rack cross pieces loose. Whenever, I got up to a certain speed, or a truck would pass me, or a really windy situation, they would bang and the sound would transmit to under the vehicle. It was sooooo weird, I am glad it is now fixed.
100% fixed. (My mother in law suggested the roof rack !)