I have what appears to be a common problem, which is a humming subwoofer in my home cinema system. After perusal of all the threads I can see it seems it's because of a 'ground loop'. I've tried the obvious things without success and can't even fathom some of the things people are talking about. Some are just too technical for me. Other things, like looking to see if my sub has an earth wire in the mains lead, can't be done becaue it is a sealed plug (or am I just beimng thick?). The simplest solution, then, seems to buy a 'ground loop isolator' but I have two questions. 1) Where do I actually stick the isolator? Between what and what? I've seen pictures of two isolatore from links on here and they both have two phono leads. 2) Is the device likely to deteriorate sound quality in any way, for example by filtering out some frequencies? By the way, my sub is a Castle Cube. Thanks.