I'm getting an intermittent clatter and/or chuffing/rubbing sound from the cylinder head on this 70,000m car. It has a full Audi service history before I bought it earlier this year, the oil, filter and cambelt have been changed in the last 6 months. The correct parts were used by an HJ recommended garage I have trusted for years.

My garage have spent some time trying to diagnose the cause by keeping the car overnight and then starting it up from cold in the morning. No clear conclusion could be made. Sometimes the noise was there and sometimes not. The clatter is pretty certainly a single hydraulic tappet which sometimes complains when the engine is hot or cold. The chuffing/rubbing sound could be the exhaust valve variable timing mechanism (oil operated) at the back end of the head. Access to this area is really hard and involves dropping the back of the engine down to get clearance.

The mechanic and I agree that it could be an oil pressure problem, but checking the pressure is an expensive fiddle involving removal of the inlet manifold to fit an adaptor to the pressure switch on the oil filter head. There is no guarantee the inlet manifold would go back on with the oil takeoff fitted. Solutions might involve a new oil pump, new pressure retention valve, cleaning the pickup strainer, or what?

Lots of maybes, any advice on how to narrow down the problem without a huge bill for diagnosis?