I just thought I'd post an update on this. This weekend I whipped a wheel off and put in the universal shim pads* on the brake pads. The noise has totally gone!
So it was definitely worth a try, for the £6.95 (approx $10) they cost.
Thanks for the help anyhow everyone!
*
http://cgi.ebay.co.uk/Universal-Sel...=item3a5e96b8f5