A few months back I noticed a faint buzzing sound whilst sitting in the back. Now that I know the sound I can always hear it whilst in the drivers seat.

I notice the buzzing sound starts at around 58-60mph.

The pitch of the buzz increases with speed.

The buzz sound doesn't change when the road surface changes. It's a very consistent sound.

I have read around and gathered that is could be the tyres, wheel bearings or fuel pump.

What are your thoughts?