Panzercat's got the right idea. You obviously have a problem. Swapping the cables around will narrow it down to either one of the cables or either the balanced output section of the preamp or the balanced input section of the power amp. If it is the cable, i would simply resolder all of the terminations using good quality solder or return them to the place of purchase if brand new. If it's not that old and you don't feel comfortable with a soldering iron, you might want to contact the manufacturer about this BUT make sure that it IS the cable first.
I recently bought a set of long (6 meter) cables from someone here on audiogon. Being a "tech" by trade, i tend to check everything out electrically before hooking it up into my system. As such, i found that one cable measured over 50 times higher in resistance compared to the other. I simply resoldered all of the connections and that took care of the problem.
When i contacted the seller, he was shocked to say the least. He asked if it was the "red" one as he always had problems with what he thought was "RFI" coming out of his right channel. He never thought to check the cables as they were "brand new" and "factory assembled" pieces. He was only able to cure the problem when he changed ALL of the cables in his system at once to a shielded design. He thought that the shielding took care of the problem when in reality it was simply a matter of finally replacing ONE defective cable.
The moral of this story is that even "new" products from "good" companies are sometimes defective out of the box. Don't take ANYTHING for granted, regardless of what name is on it or how much it cost. Being able to "troubleshoot" can save you LOTS of time, money and headaches in the long run. Just take your time and be as thorough as possible when trying to track things down. Sean