So I just bought this 06 GXP and it is pretty loud and very loud on the inside. I looked under the car and it appears to have the cat, resonator, and stock mufflers because they have a GM part number on them.

What could the owner have done to make it this loud? Also, did GM make a performance exhaust for these cars?

Thanks!

 

Well, if it appears to be stock and you can tell there's a res, cat and mufflers under there then I would check for a leak somewhere. GM didn't make a performance exhaust for the LS4 so the stock sound should be pretty "quiet" even under load.

 

Thanks for the quick reply. There is no leak, it really sounds like it is aftermarket. I will try and take a vid at lunch and post it.

 

Check for headers?

 

No headers.

 

Hmm you checked everywhere for a leak? Even where the downpipe bolts to the rear exhaust manifold? I was going to ask about headers too but someone covered that. If it was aftermarket I would think there'd be some kind of label or indication of what company it is on the mufflers/resonator.

 

Do you still have the sellers number? Lol

 

Check the top side of the mufflers. They're probably rotted through.

 

Haven't checked the top of the mufflers for rot thru but will. I am trying to have the dealer find out from the previous owner what was done. It says GM on the mufflers. Here is a video that I just took, its not the best but you should be able to hear it well enough.

http://youtu.be/66Ruma5974g

 

the second rev at about 21-24 seconds kind of sounds like something has rotted out...Not sureo n the GXP, but i can crawl under my monte and see the top of the mufflers just fine, i would try that.

If it's not the mufflers, maybe the resonator. Mine rusted out after 3 winters on my 01 Monte SS, the metal used on those isn't normally all that thick, could be that.

 

Another thing to note is the drone on the inside is definetly coming from the back of the car, it is almost unbearable when moving from a stop to about 50 mph.

 

cold start the car and have you and a friend block the exhaust with gloves and your hands, if u hear exhaust still u know you have a leak. Is the res still there? any part of the exhaust hacked up? should be flanges and bends....not clamps and mig welds....

 

Exhaust tips look welded.

 

There is a resonator on the car.

 

sounds just like mine did stock

 

I dont remember what mine sounded like stock, ditched the muffs a couple days in to having, but it does seem a lil loud to me, could be vid and distace??

 

Found the issue! Rusted seams on top of both mufflers! Damn dealer said it was performance exhaust...ha....we will see if they will cover it.

 

my car sounds exactly the same as yours and my mufflers are rotted through thats funny it sounds exactly like my gxp

 

lmao @ performance rust....

 

Got new flowmaster exhaust installed today and the improvement is 100%. We shall see if the dealer will cover the cost. $225 for 2 new 40 series installed by welding. Looks like a good job and sounds GREAT!