[Mustard3]

On turning off my car I've noticed a strange noise coming from the vacuum control area (engine bay above exhaust manifold).

The sound is an underlying hum, with a louder, irregular buzzing noise, a bit like morse code. I goes on for up to a couple of minutes until the vacuum releases and the actuator rod releases with a loud 'sigh'.

I took it to my usual BMW specialist, who after listening to it (no fault codes) said they had only come across it once before and it was a faulty large turbo actuator which can only be bought with a new turbo at a cost of £1600 fitted.

However, I removed the engine cover and scuttle panel and it appears to be coming from the rear pressure converter. You can feel it vibrating in time to the noise. Can these thing fail in that way? There is no loss in performance.

Funny thing is, that pressure converter was replaced recently by above specialist. When they did it I was expecting both to be replaced along with the modified mounting bracket, but they said it wasn't necessary. When I inspected it earlier I noticed the two PCs are of different design, and the new one does not appear to be fixed securely to the bracket, it can be twisted a bit. Odd?

I would be grateful for any thoughts on this before I go back to the garage.