I have a 2007 A6 with the 2.0tdi BRE engine, just over 116k.
I have recently noticed a weird woo-ing kind of noise from the engine, almost sounds like the engine is haunted! It only happens when the engine is warmed up. It is most noticeable at low speeds/rpm, but I think that's because there is less ambient noise. The woo starts around 1300rpm and upwards, does the same whether in gear or not.
There is no noticeable performance loss or smoke from the exhaust, the engine does seem to be using quite a bit of oil and water however - oil light has come on quite a few times. Checked the oil filler for mayonnaise, but it all looks normal. Proabaly using a litre a month or so of oil.
Any ideas what might be the problem here?