For the past month, I am hearing exhaust noise which is excessive when driving at street speeds with windows up - a droning low frequency note which eerily reminds me of my old station wagon with a rusted-through exhaust manifold.

I first started hearing the noise after the car was stranded in a flooded parking lot and the water level was mid-wheel, reaching the exhaust pipes and possibly affecting the exhaust. Went to the dealer a couple of weeks ago, and was told that the sound was caused by a rattling lleft exhaust tip which was replaced. Great, I thought it was more serious... but replacing the tip only calmed the noise a little. It is still there and is especially annoying at low revs.

I had a couple of friends ride in the car with me - both heard it, but thought it was something I could live with. But - the noise is there, and the car feels different... from the one I had a month prior. All suggestions welcome and appreciated as to where I go from here.

Additional info, if it matters - ECU reflash done 6 months ago, it is a stock 07' G35x with 19,500 miles on it. All maintenance sans oil changes done at the local dealer.

 

If the water level reached both exhaust pipes, the baffling inside both mufflers may have rusted out. I would replace both.

 

Thing is, I started hearing the noise virtually the next day - too quick for them to rust out this way. In any case, I scheduled another service appointment with the dealer and will make sure they consider this possibility.

 

What happens to hot metal when it touches cold water? It shrinks, splits, and cracks.

A bolt at a joint may have busted causing a leak...a crack in the pipe itself could have formed, a flange may have busted or a weld could have let loose. Investigate the entire exhaust system for visible flaws. If none exist, feel around the exhaust with the car running until you can feel an exhaust leak.

 

Appreciate the informative reply, will do what I can myself (although I am not that handy). If the dealer cannot find the source of the problem, I know a good mechanic that would perform a exhausto-scopy on the G

 

Have you ridden in/driven another G35 recently to compare the two? It is possible it's in your head.

When you start listening for problems, you start to hear everything (whether or not it's a problem).

An exhaust leak would sound more like a tapping/ticking sound than a drone.

Another thought is it could be a bad cat. Either way, have the dealer look for/fix the problem if there is one.

 

This is not an argument.... by any means.. but do you realize how hot that exhaust would have to be in order for it to shrink enough to cause a seem and/or bolt to break?
I was a steel worker for over 20 years so I have at least a little experience with this.
I know that our exhausts get a little hot, but not to that level. Also remember that we drive in the winter snow storms and through rain and we don't see exhaust parts shrinking and breaking.
This could be caused by water damage, sure.. but I doubt it was caused by the steel shrinking and breaking.

 

I agree it's not a likely scenario. But if water can warp a hot rotor, couldn't it also warp an exhaust enough to cause a leak at a flange?

 

I was considering "in my head" scenario and so will test drive an new 08 X at the dealership, just to rule out this possibility. Still, the car really sounds significantly different at low speeds, and the low-hz drone was heard by other people than myself. I recall commenting to myself post-break in how quiet the G was when driven at low speeds, yet how nice the exhaust note sounds when it is opened up. It is not the case anymore, and the change was sudden enough to be noticeable. The replacement of the exhaust tip did quiet things somewhat, but the drone is still there. Maybe they need to replace the other tip

 

"The world is an imperfect place. Screws fall out all the time."

I'll admit, nothing is impossible. Unlikely maybe, but I'n concede enough to say ... you never do know.