Weird noise from rear of the car.

[B-Line]

Mostly happens when car is cold, not warmed up.
It almost sounds like the low hum of a coffee grinder.
At first I thought maybe the auto lock mechanism on the hatch was running even though the hatch was closed, ruled out that though.

I think it may have something to do with the suspension.. (So what else is new ) The sound seems to change quality when I lower the suspension. It sometimes even goes away. But when the suspension re-adjusts, it comes back.

Oh yeah, I only hear it inside the car, not outside.

Any thoughts...

[Donegal TDI]

Probably stating the obvious here, but is it the air compressor running, or in that general vicinity the noise is coming from?

[adrian.b]

Also bear in mind that your ABS gear is sat just under the spare wheel in that black dome, have a listen there.