Shoulder washers will help if you end up with ground loop problems, or you can get a Hum Eliminator. Shoulder washers are about $7.20 for 100 of them. You can get them at www.datarax.com or your favorite local pro audio shop. As for a Hum Eliminator they are a bit more, about $59.00 for a two channel and about $199.00 for an eight channel. You can get them at www.interstatemusic.com or your local pro audio / recording shop. I’d try the washers first if you have a ground loop problem.