sound from trans to rear end ever 5 miles last about 5 sec.replaced u joints on 2003 Lincoln Town Car

have had lincolns 25 years and limo co. do repair not seen any thing like this before

Asked by for the 2003 Lincoln Town Car
Need more description/conditions in order to answer this. Speed , load condition, turning , straight only, gear selection make a difference? what if any diagnostics (besides u-joint replacement) has been done . Did u-joint replacement have ANY effect on symptoms?