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Rattle, vibration and knock under the rear of the car

New User
Posts: 1
Joined: 12/12
Posted: 12/11/12 08:36 PM

I have a 2008 Mustang GT; when I start the car and run it down the road cold everything is fine and the car is tight.  After about 20 minutes of running at highway speeds and after the car heats up and I slow down to less than 40mph I can hear a rattle in the rear of the car like if the exhaust is falling apart.  When I accelerate gradually and hit bumps their is a squeaky type rattle like something is loose.  When I drive over railroad tracks or bumps there is a knocking under the rear like the exhaust pipes are loose and hitting the bottom of the car.  I have had the car on a lift and can't seem to find anything loose. When the car cools back down it tightens up again.  When hot and I idle at a stoplight and shift from park to drive and the engine idles down I get a metallic vibration until I raise the RPM again.

Anybody have any ideas of what this could be?  

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Posts: 58
Joined: 04/12
Posted: 12/11/12 09:09 PM

when you put it up on the lift

was it a drive on ramp type lift.. found in muffler shops or wheel alignment shops.. so the suspension is at ride height???

loose shocks/ loose shock bushings.

broken exhaust hangers..   or stretched exhaust hangers...

bent exhaust system..  sometimes.. exhaust systems get bent because of curbing damage when  parallel parking ...  when backing into a dirt hill side...  when getting towed.. when being high centered over either a speed bump or a curb..   errant floor jack positioning..   broken motor mounts..

don't forget.. that when you get out.. the ride height changes..

look for clean areas on various parts that might show rubbing..  

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New User
Posts: 36
Joined: 03/12
Posted: 12/15/12 04:16 AM


See if the baffles in the mufflers are loose. They can drive you crazy. Try and have the car sitting on the tires and get under it and take some wrenches with you, and bang with your fist on the exhaust. Sometime shock bushings break and the shock will rattle in the support...


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New User
Posts: 1
Joined: 01/13
Posted: 01/05/13 07:17 PM

There is a bracket located just in front and above the differential u-joint. One bolt comes down from under the back seat and 2 bolts go up from underneath. You can barely see them above the diff when the car is on a hoist (2 poster suspension hanging free), This bracket will loosen off and cause this exact problem, ask me how I know!  

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