Sounds like a vacuum leak
 

I took the car out of hibernation today and noticed an odd sound when blipping the throttle from outside of the car, not noticeable inside.

No error codes showing, you can only hear it with a sharp/hard blip of the throttle, ie high vacuum entering the intake tube.

Any thoughts, sounds like its coming from around the throttle body. I think I will have to dig out my smoke machine.

I'll also get Kim to blip the throttle so I can get closer to try to find the source, a bit tricky from behind the door.

Sounds almost like a zipping or ratchet noise.
Likely a dumb question, but what happens if you blip the throttle with just the ignition on?

Thanks Michael, I didn't manage to persuade Kim out to the garage last night, so made up a to do list for today, your suggestion was first on the list.

Ok just been out to the car again. I'm now thinking that its actually noise from the gears in the throttle body, perhaps its always been like that or maybe its getting worse.

I was curious as the TB on mine makes a gentle buzz that varies slightly when the throttle is pressed. I hadn't heard it until fairly recently and wondered if it was something new. I'm guessing that I was just being my usual less-than-observant self...

I've just tried the same manoeuvre as you with very similar results. Somewhat quieter - but I didn't have the air intake off, so yours is likely normal.