Tapping/whistling/wheezing noise from TD4 engine

Hi folks, bit of weird noise coming from the front left as you look under the bonnet. It's a sort of tappy/whistly/wheezy noise that can be heard from inside the cabin whilst driving. No change on accel/brake just always there.

Parked it up and popped the bonnet, when listening to the area the noise appeared to be emanating from there also appeared to be what sounded like the noise a foot pump makes?? Make any sense??

I checked the Haynes and it suggests faults more common on petrol engines, so anyone got any ideas?

Regards
Riki

If you were having power losses the 'foot pump' noises could be compressed air escaping from the intercooler? I would also check the drive belts etc as they make some strange noises occasionally.