[Chaz]

Originally Posted by snapdragon

Back of engine..possibly and hopefully vacuum pump.
Just guessing but worth a closer check?

https://www.youtube.com/watch?v=U2PZ4Xklx38
https://www.youtube.com/watch?v=yYlz9pDzfsY

I took a quick look. Arent all the 4.2 TDI engine ancillaries around the front of the engine? The sound 'seems' to come from the rear, so not sure.