Humming noise on startup

[chris24]

A few times during the recent heatwave in the UK, my IS300 comes up with a humming noise on startup (before the petrol engine kicks in). I can hear the noise still buzzing/humming along with the petrol motor for a few seconds after driving off and then it stops. I've a feeling this is nothing to worry about and that I may have come across it years ago on a Prius. Does this make sense to anyone? Can't find any help in owners' manual.

Thanks

Chris

 

[PaulWhitt20]

Cooling fan on the Battery ?

[NemesisUK]

The electric compressor for the aircon?

[ColinBarber]

It is probably the brake accumulator electric pump pressurising the system and is perfectly normal.

[NemesisUK]

6 minutes ago, ColinBarber said:

It is probably the brake accumulator electric pump pressurising the system and is perfectly normal.

I usually hear the one on my car as soon as I open the driver's door, only last a few seconds.

The aircon only comes on when the hybrid system is started.

[ColinBarber]

1 minute ago, NemesisUK said:

I usually hear the one on my car as soon as I open the driver's door, only last a few seconds.

The aircon only comes on when the hybrid system is started.

Agreed, but the compressor wouldn't turn off after only a few seconds though.