Yesterday whilst on my way home from the MOT centre my car developed a strange noise. It sounded as if i was dragging something up the road so i pulled over and had a good look round the car and everything seemed fine. I opened the bonnet and there is a noise at the back of the engine near the air intake which sounds 10 times worse inside the car. Its very hard to explain the noise, it sounds like a pump or something maybe broken. The noise doesnt speed up or slow down with revs nor does it affected by the power steering or heating. Its a continuous noise from cold start. Anyone got any ideas what the problem could be?