Car: Octavia 2 Pre FL 1.9PD Elegance 2008 Model year - registered 2009.

When I switch off, what I presume to be the ABS pump occasionally buzzes on for a while – usually it does not.

When I come back to the car, after some time, usually there is braking assistance without turning on engine but occasionally need to start up for assistance to return.

Presume this is all a function of how much pressure is in a reservoir somewhere, but is this normal?

ABS light comes on then goes off and stays off as it should.

it all sounds normal to me. The buzzing sound will not be the ABS pump, I bet its the flap motors inside the dash closing the vents which is what my Audi does.

My 2008 vRS emits an electrical buzzing noise for approx. 20 seconds after turning off the engine.

Mine does it too always has. Used to sqeak as well but it's gotten bored of that and stopped.

Might be the Intake Manifold Flap you are hearing. When you shut off the PD engine this flap closes to cut off the air to the engine intake. This provides a smooth engine shutdown, rather than a nasty jolt.

Could be that flat holding closed you are hearing. It does it on mine when switched off.

Both of my Elegance Octavia II's (1 diesel pre FL, 1 petrol FL) have made various whirring, buzzing, ticking sounds on start up and shut down. Combination of fuel pump and climatronic I think.

sounds perfectly normal.

My vrs does that kind of thing, also my works van which is a 61 plate caddy makes a buzzing noise when you turn it off