It was the turbo on the old Scenic RX4 (a common problem apparently due to oil starvation) and it nearly blew up just as my wife got to the garage. It's going to cost a lot to put right unfortunately, so not a great day.
On the plus side I acquired a petrol generator that needs a little TLC after getting soaked in a winter flood. A bit of a strip down, a good clean and some WD40 and hopefully we'll get it back to life.
More of the buggy.