Could be a shaft. I have the same thing, and my shaft is very loose.
Jason G. Replaced 1st intake manifold at 15. haha
'03 Marquis: 67K,15.31 @ 91.19, MZT 93 octane tune, P&P Aviator T/B, duals with rear cats missing, 3.27 Trac loc 31 spline rear, sway bars, tints, badgeless grille..blahblah various exterior mods *NEW* Steeda pulleys and Towncar rims
'08 F-450 6.4 Powerstroke: DPF,EGR delete, Spartan powered tuner.