Ok so today i changed the rear wheel bearings! Nice easy job to be fair, best way to do it is with a press, but i used a heavy mallet to smash the old bearings out and using the outer race of one of the old bearings drifted the news ones in with the mallet, the new ones went in alot easier than the old ones came out.
All great now no howling/whiring what soever - On closer inspection of the bearings they were showing signs of discolouring (aka going yellow). This was because the grease that was in the bearings had started to harden/fail and therefore the bearings were getting hot/making noise.
I think the failure on mine was purely because of the lubrication not doing its job properly rather that technical fault with the mechanical components of the bearings as there was no sign of metallic pick-up or such