Read the post in "general" about chokes..I've bought them. In my opinion that is not your problem. Since we're talking 3rd party here I'll tell you they are about the same price as the phone for end of line chokes. Part number is in the other post.
If this were AC power induction you would have it no matter what. Wouldn't matter if one line or 10 lines were hooked up, you have it on each line. Like I said, you have more trouble shooting to do.
