Since I've been able to remove the cable from the interference I would have to move the new cable to a location where the interference is present. So I would first have to move things around to pick up the interference again and then try it with the new cables. I'm willing to do this when I get some time.

Ericjb, when you say you have a shielded cable made up what cable are you using? While CAT5 UTP cable seems to be the preferred choice for many of you it is, in reality, not shielded cable. All though it does have inherrent properties that help it minimize EMI/RFI interference. Are you using STP cable?