peugeot 307 1.4 hdi 'whirring' noise

beeedant

car's making a fairly constant whirring noise while driving around local, though it's fine on the motorways. my friend said it's 'just' the fuel pump starting up when he heard it when i started the car next to him... but it doesn't go off while i'm driving around and is worse when going up hills.

i really can't afford to have any more work done on the car after having already paid out to have belts and waterpump replaced when i first bought it, and a new clutch fairly recently. guess i'm just after hoping it's either a (cheap) easy fix... or it's not something that'll lead to irreparable damage to the whole engine if i leave it till i can afford to get it sorted!