Flowmaster Vibration

I know what you mean. the same thing happened in my 89 gt with flowmasters and off road h pipe but it seamed like all the body panels vibrated like crazy around 1800-2500 rpm which was really annoying.
now in my 95 cobra its even worse since I have macs with dumps. I get annoyed and just hold the button on the e brake because it rattles so much

similar problem, simple fix. the pipe leading from my H to the muffler was rattling against the underside of my car. specifically the passenger side floor board. Just get under there with a pencil and place it between the pipes and anything your exhaust pipe COULD ever possibly touch and place the pencil in between the two. If the pencil dosent fit in a certain spot that may be where its vibrating against. THe pencil (over) compensates for the pipes vibration and its a simple yet effective method to pinpointing the problem. Hope this helps.

You might be able to adjust the tension on the brake until it goes away.

I have the EXACT same problem. and so far the only fix I can figure is (and I do this) it I drive with my hand on the emergency brake, or at least I kinda grip the base of the handle so it doesn't vibrate. I have been thinking of putting a rubber wedge between the handle and the console since wedging my finger in there stops the rattle, but haven't gotten around to it yet since it is so easy to just drive with my hand down there. But it does suck and the only explination for me is that it is a crapy plastic piece with lots of play. Sounds like the spring inside is rattiling loose.

Guys--

I am glad its a common problem. I wanted to make sure it wasn't something tearing up the car.

A piece of rubber wedge between the console and handle sounds like it might work....never thought of that...Thanks

V6JonesMustang

had the same problem. looked under the car and noticed they welded a bracket on the emergency brake plate under neath the car, so that might be your problem. cause it would rattle when you shift, so check that out

I don't know if this is exactly your problem, but the thing with mine is the spring inside rattles like a slinky in a tin can. The wierd thing is that if my leg touches the handle, it rattles, if I leave it alone it sometimes stops. If I place a finger betewen the brake and the console, it completly goes away.

ya same thing almost, i have 2 super 40's and it had that rattle when it got to its loudest which concerned me, i took it to the shop i got it done at and we banged all around every weld and checked all the clearence gaps between the underside of the car to the exhaust, it turned out that the rattle was from the mufflers cause since its a v6 the muffler just had a lot of vibrations to i cant really do anything about it, as for the vibration in the car, i dont get much sometimes on my dash here and there but i just tap it then it goes away nothing else though so if anything check the clearence around the exhuast pipe to the car.