2000 Grand Marquis noise in rear of car

Hi, I am a new member looking for some help to resolve a noise problem. I just purchased a 2000 Mercury Grand Marquis with 83K miles. I have a thumping noise in the rear of the car when going over bumps in the road. I can recreate the noise; with the rear of the car up on ramps and the bottom of the shocks disconnected (to make it easy to bounce) when I bounce the rear up & down I hear the noise, it sounds like it is comming from the fuel tank, but not sure. I did find a TSB #14181 NHTSA #620304 which talks about a clunking noise that may be caused by the "fill limiting valve in the tank" but this car was built after 12 - 1999. The TSB did not say how to fix the problem. Any help would be appreciated, Thanks, Bob

Start by physically checking all around the area for loose parts. Sometimes road salt will rust out a bolt and the piece starts to bounce around making noise. If you have definitely pin pointed it to the fuel tank, get a pro to check it out.

I have checked for loose parts several times; I did replace the insulators for the exhaust system and installed new rear brake pads.....still have noise. The car is from Florida so there is minimal rust. I had the fuel tank out of the car, inspected it but everything looks OK. I am thinking about removing the fill tube and cuting off the "fill limiting valve" which is at the end of the tube?????????

Well, here is "the rest of the story". After receiving no help from Ford Motor Co. (local dealer and the 800 #) I filled out the form on the National Highway Traffic Safety Administration web site to get the details about Ford TSB #14181. The person on the phone said there could be a charge up to $40.00 for the information. I received the details in the (snail) mail in less than one week and the good part was there was no charge. The TSB said I needed service kit F8AZ-9B246-AA which includes 1 fuel tank vapor control valve, 1 clamp, 2 studs and nuts for the tank straps, and instructions. Keep in mind now, this TSB is for 1998-2000 Crown Vic, GM, & Town Cars built up to December of 1999. My car was built in March of 2000!!! Since the description fits my noise problem to a "T' I was going to get the service kit. I called my local Ford dealer only to find out that the part (after 10 years) is now obsolete. I was able to find the part at Green Sales Co. in Cincinnati and the price was half of what it was at a Ford dealer that did have the obsolete part. After receiving the kit I removed the tank for the second time and installed the valve in the top of the tank. No more noise!