Honking Noise under Hard Acceleration
 

The D3 ZF gearbox can occasionally suffer from poor shifting and a 'honk' noise under hard acceleration. As per the D2 gearbox it does need servicing every few years or 50k miles. Audi actually acknowledge this now.

Unfortunately the filter is built into the gearbox so cannot be changed as per the older ZF 5 Speed Tiptronic though the procedure is very simular.

Use a decent gearbox specialist who understand the box and that it will require a full flush of transmission fluid, not just a change.

See Ian's post for recommended specialists. Unless you have done this before yourself, I would personally pay someone £130 to do it (Approx).