Ok, this is a new one, has been happening for about 2 weeks, the car's an Octavia vRS 03 reg, with 58,000 miles on it.

I can hear a "bubbling" or cracking noise coming from the gearstick area, or possibly the passenger footwell, when I listen closely I think it's something electro-mechanical, sounds like maybe a pump or something starting and stopping all the time.

It's present whenever the engine is on, moving, stationery, climate control on or off. I'm due for a service in 3 weeks so I can get it checked out then, but does anybody know what this might be ?

Might be the fan for the interior temp sensor in the climate unit

Decent theory, although it still happens with the climate off ? Will mention it to dealer at service.