does this happen when parked or moving? if only when moving, you should inspect your driveshaft for interference, check the rubber flanges on the driveshaft and the support bearing on the driveshaft as it is tied directly to the passenger floor at the tunnel.

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)