1994 Mercury Sable front end problems

Noises problem
1994 Mercury Sable Automatic 39545 miles

I FEEL & HEAR a thumping when I am driving. It doesnt happen all the time. I can feel something moving in the front end and I can feel it when I press on both the gas and the break. You can really hear it once I've stopped and whatever is moving up front continues to move. You can tell it is rubber or plastic and it is coming from right up front in my car by the pedals and back where my ashtray ends. Sometimes I get the faintest smell of burnt rubber. I had my suspension check and front brakes, and they all checked out. Please help no one can figure it out, because of course when someone else drives it it doesn't do it.