Ok, I am just curious if this is normal or not. My car has 58K miles on it and is an 06. The only drive train mod I have done to the car is a GT muffler, everything else is stock. My car is an auto, and when you have it in drive while sitting at a light or something it likes to vibrate. Not really bad, but more than any other newer car I have driven. When you put it into neutral the vibration goes away. Also the RPMs drop when the cooling fan comes on and really makes the car vibrate for a few seconds. Does everybody elses car do this too or is it something wrong with mine. I was reading a little bit and I am under the assumption that I have some worn motor mounts or something because the car runs and idles great.. I Have brand new spark plugs in it..

 

My car does this too, but it is pretty subtle, so I never worried about it.

 

Thats normal mine does the same, also it probably makes worse vibrations with an auto!

 

I started noticing the vibration when I had the duals put on. I thought maybe the shop had not installed it properly because the vibration goes away in neutral. I have learned to live with it, or put it in neutral at a light.

 

mine does it too, also I have just a GT take-off muffler

 

Mine does this too. It started after i put duals on it. I just live with it. There are a few threads on this from a couple years ago about this issue. I notice it when the A/C is on or the Defroster is on, typically anytime the compressor turns on.
there was a TSB back in 05-06 on rattles at the trans mount exhaust hanger. (these are no longer put on the cars, and were location mounts). The tsb fix was to cut the hangers off. The TSB also said to loosen the manifold bolts and let the exhaust hang free then re-tighten.
I suspect when we change out our exhausts we put pressure on the system and this loosen, re-tighten may help. I haven't worried about it enough to try it.
If you try it let me know how it works

 

Is the muffler rubbing the bumper at all? Mine did at first when I did my exhaust (drove me NUTS) and I trimmed around it and it stopped.

 

thats a good point to check too. In my case its not rubbing.

 

I figured it was something everybody's car does. I am just being picky, I put in fresh Mobil 1 fully synthetic, motorcraft filter, and I changed the fuel filter yesterday. Runs a little bit smoother, but it might be just me lol.

 

Lol its probably in your head although changing the fuel filter should be slightly noticeable, especially if you haven't changed it in some time!