72 Mustang Weird Noise

[Hawkk72]

When my 72 fastback (302, auto, 4bbl) is idling there is a loud thumping noise almost like something hitting the floorboard of the car. Seems to be on the passenger side, but I cannot for the life of me find what's causing the noise. This doesn't happen all the time but frequently enough to be a cause for concern. HELP!

 

[geostang351]

When my 72 fastback (302, auto, 4bbl) is idling there is a loud thumping noise almost like something hitting the floorboard of the car. Seems to be on the passenger side, but I cannot for the life of me find what's causing the noise. This doesn't happen all the time but frequently enough to be a cause for concern. HELP!

My quess would be the exhaust sytstem at the collector/pipe joint. My car does it sometimes too. There is nothing securing the the exhaust system from the headers (Where they are secured at the block) to behind the muffler at the rear axle. As the motor moves slightly the exhuast is probably bumbing the tranny tunnel, floor pan or frame rail.

 

[DJCarbine]

Same thing on my 66. The aftermarket trans mount and stock exaust pipe hit at idle, causing a thumping sound. Check for clearances under the car and look for any rubbing