So I just had a magnaflow muffler installed about a week ago, had a local shop I always go to to just replace the stock muffler with a magnaflow and a black exhaust tip everything else remained stock. Love the muffler and new sound. Though when I' am sitting at a red light or stop sign the truck starts vibrating like I'm driving a 7.3L turbo diesel, the rpm's are not bouncing up and down they remain at a low constant rpm like they should be but I have the annoying vibration. If I put the truck in neutral though the vibration will go away until I put it back in drive, again the rpm levels remain the same. I have highly unlikely doubts that it is from the new muffler but I can't figure out what else it could be from since this problem did not occur pre installation. Any thoughts or idea's on the problem?

 

Seems odd. The only thing I can think of is the muffler shop hung the new muffler without a rubber isolator. That would transfer extra vibration from the exhaust to the vehicle.

 

It's not as simple as that .You have changed the weight for one thing and perhaps other things too. That will change vibration frequency peaks and amplitude. First make sure you have the proper vibration isolators . Then go back to the installer and see if they can improve things by changing things .It might take only a small change to do it.