2003 V40 2.0 Auto. The sound is from the driver side of the engine. Sounds like it might be some air escaping or being vented. Whilst the engine is making its regular injector or valve like tick, tick, tick, tick, tick, tick, tick, tick, tick, etc. this sounds is like a cat purring at a slower rate, prrrr,prrrr,,,,,,,,,,,,,,prrrr,prrrr,,,,,,,,,,,,,,,,prrrr,prrrr,,,,,,,,,,,,,etc. Not very loud, not very noticeable, but unusual. What is it? Thanks. Lothar.

SOURCE: Buzz

This sounds normal. The engine cooling fan it set to contine to run after being shutoff. If you open the hood at some point and look at the layout, you will see the electric radiator fan in the front of the engine compartment, along with a note that says: caution fan may run w/o vehicle on.

SOURCE: noise

Some models have a vacuum pump that operates at times. I believe it is to help provide more vacuum for the power assist brakes.

Does it happen when you are stopped, and you depress the brake pedal a few times? Does it happen when the engine is cold, or warmed up?

Bret
RepairPal.com

SOURCE: 98 Volvo V70 GLT - Oil Pump or Valve Job?

Most common cause of ticking in these is the oil pick-up seals. Remove the pan and replace the oil pick-up tube seal, the two seals for the tube in the pan and the 2 O-rings on the right side of the pan. And dont use silicone to seal the pan back up, because it WILL leak, I highly recommend the Volvo sealant

SOURCE: Driver side door making a popping noise when

Check spacing between the front of the door and the
fender. The door could be pinching the fender when you open and close it. Hope this helps.

SOURCE: Drivers side vents blow hot

Hi!!
The Air Blend Door Actuator on the blower housing, under dash, passenger side is stuck or defective. The actuator controls the flow of air from the Heater or AC, depends on your settings, if the door is stuck in between, warm air from the Heater will go thru. In your case, door is open just a little or better said, it is not shut all the way, allowing warm air thru only some of the ducts, that unfortunately, happen to be the driver's side.
Try activating the door by setting he temp control from cool to hot a few times to see if the door actuator will get released, if it does not fix the problem, the actuator will need to be removed for closer inspection and if faulty replaced.
Good Luck!! Don't forget to rate this post!!