Squealing / Squeaking noise under power, HELP?

[myfirstseat]

Hi guys, I've tried the forum search but cannot find what I'm looking for. I have a squeak / squealing noise under acceleration. There is no noise at idle and no noise whilst moving the steering wheel or any other time apart from under load, whether it be under light acceleration or otherwise. Is this simply a belt or would i need to go about replacing the belt tensioner or something else? Its very annoying however does not seem to affect the way the car drives. Any help would be appreciated.

P.S This is a PD150 ARL coded TDI.

Thanks