Odd engine noise at tickover/just above tickover

Hi all,

I've noticed this odd noise on the Mrs' car that is getting steadily louder. I first noticed it at the end of last summer and I'll try to get a recording off it but it varies with engine speed and sounds more like a "whup whup" noise than a "tap tap". At higher revs (above 1000?) the noise is not particularly evident. Not sure if it is a tappet or water pump, perhaps? 

The engine has done about 69k (1.2 TSI 86) and has had regular (6-10 month) oil changes due to it being used for short trips.

Any ideas? 

Cheers.