my 1997 grand marquis has two issues. first, when the engine is under a load it has a rattle similar to a pre ignition sound and second, I'm hearing a thump from the rear of the car that could be the fuel pump. I listen to the fuel filler door and don't hear it and it seems a lot more noticeable in the interior. so far as the rattle goes it seems worse as you drive it but at idle it goes away. if the car is in park and you rev the engine it makes no noise and runs very smooth. At a loss and needing help

 

The rubber hanger rot out and makes the exhaust hit the floor board if that's it it's an easy fix.