I just bought a 503 head too...I don't recall hearing any noises but I wasn't paying much attention in particular. Will check it more tonight when I get home.
Not sure if this helps / is obvious/ is even your problem, but my 503 was making a scraping sound during pan, and it turns out that the little curved piece of metal that pushes up against the base for the pan lock, is a little loose in its single point of attachment, and was leaning to one side, dragging on the base, even when it was unlocked. I just pushed it back into place, and it fixed the problem.