Ground Loop Isolators are less than desirable - they fuck with the audio signal, rather than fucking with the electrical signal, so your overall audio quality can be made worse. If the GLI uses cheap components (or is poorly made), it will attenuate both the bass and/or treble frequencies... And then you'd just have drums with a bit of midrange bass!
My laptop has an RF transmission problem (and its power supply has a floating earth), so what I ended up doing was isolating the earth pin on the power supply by coating it in sticky tape. In clubs, where DJs use their laptops (e.g. with Final Scratch or Serato) this is a common problem, so clubs increasingly have 'sacrificed' fourways - the earth pin is disconnected and is there purely to open the safety shutter in the socket it's plugged into.
You can't do this for all equipment, but if you're running your audio kit off several plugs, try to run them all the same fourway - decks, mixer and PC. This will reduce / minimise earth hum, but might not remove it... If you have poor wiring in your house, you're pretty much screwed.
It sounds like some of your kit isn't earthed properly though, check your wiring and earth connections.
The GLI may be a quick fix, but your sound quality will quite possibly be degraded as a result - just be aware of that. Certainly a £5 GLI will not be great quality, if it's selling for £5 then it probably cost £2 (or less) to make. There's a reason some GLIs cost more than £80/£90...
