2001 V40 Noise
 

Just bought a 2001 V40 with 47K, good little family car for us.

Noticed that when driving very slow, like parking lot/driveway speed there is a weird noise that occurs. It's not a rattle or anything constant, it is like a "booooonga" that lasts for bout 1.5 seconds then nothing for a few seconds then it goes again. It's always the exact same pitch, as if it's some sort of indicator but I have no lights on in the dash panel. It seems to be coming from the engine compartment somewhere but I'm stumped.

Can someone explain this strange sound?

Also... why don't the replacement bulbs for brake (stop) lights that Auto Zone has work?? We tried two different bulbs that fit, were 12v 5w and neither worked. The reverse light swapped into the brake light slot works though.

TIA for the help. Searched a bit but have limited time to look.

RE: 2001 V40 Noise
 

Are the Brake pads low?

RE: 2001 V40 Noise
 

Sounds like the ABS pump to me- mine does this too with no ill effects.