Has anyone ever heard this one......

Ive been hearing a "clank" sound from somewhere underneath my 97 F150 2x4, stock wheels, for about a month. It happens everytime I just start out or come to a stop. Pulled the wheels, checked everything I could think of...all seemed tight. Finally broke down and took it to the dealer today. They first tried to feed me the usual BS...rock in the wheel..loose mounts, etc..Till they heard it. Turns out they say the lugnuts are slipping and the sound I'm hearing is the wheel/lugs sliding when I'm starting or stopping. Didn't sound right to me but sure enough...looks like there sliding (wear marks). They're all torqued to 100lbs. Now gwt this..they recommended I put on tapered lugnuts I had the nuts replaced when they we recalled because the old ones were known for comming loose!!

Whataya think??