Loud humming when I connect my DVD player

Your interconnects may have a broken ground. Have you tried another pair? Are the DVD prayer and Preamp plugged into the same outlet? If not: One outlet may be wired incorrectly, with regard to hot and neutral. Try reversing the phase on the DVD player(flip the plug in the socket).

I assume the DVD player is connected to a TV....
Is the TV connected to a CATV system? If so you are experiencing a ground loop. Disconnect the incoming CATV coax cable from the cable box and then check for hum.
Post back results of test.

Tried all but nothing worked except disconnecting the TV from the CATV box. So either the box or the cable is the issue. Anything I can do about this?