Probable electrical problem.

[tiptonian]

I think we have an electrical issue with our Passat. What I know is:

At the weekend while in Cardiff, the engine would not start and it got weaker at each attempt. The battery was nearly 10 years old so replacing it was a no-brainer, but it was still concerning that it had failed so suddenly.
Replaced it with a Yuasa 5000 series from Halfords. WHen I connected the new battery there was noticeable sparking when the + connector first touched the battery terminal and I could hear some apparent electric motor noises starting up.
It got us back to Coventry OK with no warnings about the alternator or anything.
When we stopped and turned off though there was still noise of an electrical motor running, rather louder now and loudest around the rear wheels, slightly more so on the driver side. Left it for a couple of hours to cool down but could still hear this motor noise, but not as loud as when it was hot.
To avoid risking discharging the new battery I lifted the +ve terminal overnight.
This morning I connected the battery back through a digital meter. Again electric motor noises started and the meter showed over 11A DC from the battery. The current did drift down very slightly but I could only leave it connected for a few seconds without risking overheating my meter. I'm going to borrow a high current meter so that I can see if the current drops off after all the systems finish initialising and to give me a chance to pinpoint the source of the noise.

I'm expecting it will need to go to the main dealer for proper diagnosis and repair , but any thoughts on what it might be please?

It's a 2008 B6 saloon with 1.8TSI petrol engine