2001 Corsa C making strange sound

For over a week now when I've been driving I'll intermittently get a screeching sound that will come and go. It's definitely not just squeaky breaks because I get it when driving using only the accelerator as well as braking, the only thing that seems to stop it is stopping the car so it's not moving (with or without the engine on). It seems to be coming from the left side only, I don't know what may be causing it.

It's difficult to describe so I recorded it and uploaded an extract here:
http://www20.zippyshare.com/v/23183060/file.html
(108k MP3). Any advice appreciated.