Hmmm, no screw at all? contact axiom and have them send you one if it is really missing. screwing it in will likely not solve the problem (unscrewing it usually does the trick) but you should have a screw there so you have the option of screwing or unscrewing it.

Do you have cable TV service? I had a ground loop from my cable line and purchasing the axiom ground isolator did the trick.

-David