Ground loop isolator is to help get rid of the extra noise from something not being grounded. Some aftermarket stereos due this and it is a whine when the engine spins faster (from the alternator). What you need is a line output converter like this one:
Scosche - 2-Channel Adjustable Line-Out Converter - Clear - LOC80
Scosche - 2-Channel Adjustable Line-Out Converter - Clear - LOC80