My truck was involved in an accident. As part of the repair, a Magnaflow catback was installed. All the exhaust damage was supposedly isolated to the muffler and back.

Now that the Magnaflow is installed, the exhaust is very loud and I am hearing a TREMENDOUS amount of drone or resonance. It is really bad around 2000 rpm. Cruising at 70mph is literally painful. The whole cab resonates. It would be difficult to have a conversation at highway speed. Also, the sound seems to be coming more from the left side of the vehicle, not the right where the exhaust exits.

I chose the Magnaflow because it was supposed to be quieter than the Flowmaster and have no drone. Is this amount of drone/resonance normal with this exhaust or could another part of the exhaust system be damaged? I peeked under the truck and didn't see any obvious damage.

BTW, 05 QC w/ 5.7.

 

Pretty common. I had a MagnaFlow 14589 installed on mine, and the drone just kept getting worse. Called MagnaFlow about five times, and finally realized they did not have a clue after they originally ensured me there would be no drone.

I now have a DynoMax muffler on, no drone.

 

After a little reading (which I should have done first), I have found that the resonator is after the Y-pipe andmuffleron the 2005 and was removed along with the muffler with the Magnaflow catback install. I guess that is where the resonance/drone is coming from. Has anyone reinstalled a resonator after putting in a catback? Where? DIY or muffler shop?

 

You should have bought a Gibson.
[8D]

 

I have a Magnflow SI/DO. It does have some resonance but a Magnaflow is quiet in respect to others. I love my Magnaflow. I guess beauty is in the ear of the beholder. If you go with Flow or Gibson be forewarned they generally are louder than Magnaflow. Aftermarket exhausts aren't for everyone...

 

I don't know if the Gibson mufflers are any better. I tried 2 different versions of their "single" exhaust muffler and both had a drone/resonance so loud I put my original muffler and resonator back on and never went back. I have seen a post a while back were a guy said that if you extend the tailpipe straight back with a length of at least 44-45 inches, the resonance in the cab is significantly reduced.

 

Not sure what the resonance would sound like, but I have the Magnaflow cat back system, with both resonators removed and it sounds ground. Not at loud as flow master unless you rug it.

I can ride all day at 2000 rpm and you can hardly hear the exhaust. It has a nice mellow tune, again until you rug it.

When I do accellerate you can hear it in the cab like it's underneath you, but I can easily have a conversation with someone beside me or on the cell phone. I ran the tailpipe in the same position as the stock tailpipe with a 10" tip. 3" diameter from the cats to the tip.

Maybe I have a different muffler? How many options are there with a 3" in/out muffler?

Also, the MDS feature on the 06's might have something to do with the difference in sound between our trucks? Because when mine settles down into a cruising speed it is as if someone has plugged my exhaust since it's only running on 4 cyl's. But anything of 2000rpm and she comes alive.

 

See, that's what's weird. I don't mind the loud exhaust. I wanted a mean sounding exhaust when I get on it. What is killing me is the drone anytime the engine is between 1800 and 2300 rpm. I mean, the whole cab vibrates. I can even feel it in the steering wheel!!! I can't hear myself think, let alone carry on a conversation. I even have to turn the stereo up!! Based on what others have said on this forum, this just doesn't sound right. I am thinking of installing an Aero resonator just before the muffler (the only place it would fit) to try to calm down the drone. I know that would kill some of what I bought the exhaust for in the first place but I am about ready to rip this thing off and put a stock back on. My buddy has FM on his 2004 and it sounds nothing like this. HELP!!!

 

I installed a flowmaster 50hd,left the resonator on and have a nice mellow exhaust at idle and cruise,boy it sounds awesome when you mash on it. My friend has the Borla muffler on his,its louder than mine,but does not have any cab resonance

 

Possibly an exhaust leak or bad fitting under the cab? Shouldn't need a resonator... to me those seem to be for EPA regulations etc.