A ground loop occurs when a connection to ground is made through an interfering electrical conductor. When currents of above approximately 50 Hz flow through these multiple paths, noise occurs.
An isolator prevents the noise by breaking the loop. It is connected by phono cables and positioned between audio connections, with installation only taking about two minutes. It is used in cars and home entertainment systems, and also by professional DJs. As no battery is used, it can be left as part of an audio system at all times.
These devices can be purchased from most retail audio stores or online, with costs starting at about $15 as of January 2010.