This rumor comes from Chris Mortensen at ESPN:
Cadillac Williams finalizing deal with RAMS today.
Carnell Williams (AKA “Cadillac”) served as the Tampa Bay Bucs’ third-down back last season, and he’s an above average back at pass blocking and catching. While he has been around the league for a number of years and is approaching 30-years-old, he’s still likely the Bucs’ most dependable option as a third-down back. The Bucs do have a number of young players in camp trying out for the role – Kregg Lumpkin and Allen Bradford – but they would be a stronger team if they could get Williams to return.
It sounds as though nothing is finalized yet, but it had been rumored recently that Williams was receiving interest from the St. Louis Rams. If he were to go elsewhere, it would be a blow to the Bucs’ depth chart.