Change in Exhaust Tone 2100 - 2500 RPM
07-29-2020, 07:32 PM
#1
Intermediate
Thread Starter
Change in Exhaust Tone 2100 - 2500 RPM
I've got a strange situation that I can't figure out and have never heard before. I've got a 2011 CTT with the HHR secondary bypass pipes but everything else is stock. A couple of weeks ago while towing my boat home from the lake, the exhaust started making a different noise. Its a very distinctive and sudden change but only happens under certain conditions. It sounds almost like a valve opens and the exhaust gets loud and much harsher. It almost sounds like a machine gun or something as weird as that sounds.
After I unhooked the boat, it didn't come back for the next week so I thought maybe I'd gotten a little water in the muffler or something while loading the boat. But then we took the boat on a 3 1/2 trip to the cabin and it was doing the same thing. Once again, after unhooking it, it stopped and didn't come back until the return trip a week later with the boat attached. Oddly, it wasn't as pronounced on the trip home and for the first hour of the trip, it only did it slightly but did get worse through the trip. I should say the trip to the cabin was 92F+ and the trip home was about 20 degrees cooler. After returning home, I'm now able to get it to happen slightly while driving around without the trailer.
So here are the conditions that seem to trigger it:
Under load, 1/3 to 1/2 throttle.
Much more prevalent when towing my 5000lb boat but now seems to happen slightly not towing.
It starts about 2000 - 2100 RPM and stops around 2500 - 2600 RPM
When I've watched it, boost is 5 - 6 PSI
Adding more or less throttle or downshifting makes it stop instantly.
I haven't noticed any difference in the driveability/power.
The only other issue happening is a P0458 (EVAP Purge Valve) that's been happening occasionally for a while
Any ideas?
After I unhooked the boat, it didn't come back for the next week so I thought maybe I'd gotten a little water in the muffler or something while loading the boat. But then we took the boat on a 3 1/2 trip to the cabin and it was doing the same thing. Once again, after unhooking it, it stopped and didn't come back until the return trip a week later with the boat attached. Oddly, it wasn't as pronounced on the trip home and for the first hour of the trip, it only did it slightly but did get worse through the trip. I should say the trip to the cabin was 92F+ and the trip home was about 20 degrees cooler. After returning home, I'm now able to get it to happen slightly while driving around without the trailer.
So here are the conditions that seem to trigger it:
Under load, 1/3 to 1/2 throttle.
Much more prevalent when towing my 5000lb boat but now seems to happen slightly not towing.
It starts about 2000 - 2100 RPM and stops around 2500 - 2600 RPM
When I've watched it, boost is 5 - 6 PSI
Adding more or less throttle or downshifting makes it stop instantly.
I haven't noticed any difference in the driveability/power.
The only other issue happening is a P0458 (EVAP Purge Valve) that's been happening occasionally for a while
Any ideas?
08-02-2020, 10:57 AM
#3
Rennlist Member
Sounds like vibration and the exhaust is loose. Make sure it's torqued to spec. We installed a system on my buddies car, tightened the crap out of it and within a few weeks it started rattling. Although we tightened it as much as we could, it wasn't until we took a torque wrench to it that it subsided. We didn't have it tightened enough.
