I have just bought a 1999 V70 AWD estate in excellent condition with just 71000 miles on the clock, everything seems fine but there is an occasional loud pop noise that sounds like it originates from under the dash on the passenger side, the first time it happened I thought a stone had bounced off the windscreen, the noise was very similar to that, I contacted the former owner and he said he had heard the noise to but forgot to mention it to the garage at the last service. Has anyone had the same experiance or got an idea of what is causing it? many thanks.

 

My 2000 does the same but it always sounds like it's coming from the driver's side to me. I will say, however, that since the temps have climbed into the 60's (F) and above, I have not heard it.

 

Could be the dash mounting tabs have broken and its just your dash board bouncing around when you hit a bump. Look in the S70 forum and there is a write up on how to repair.

 

Quick possible answer: 2 possibilities.
1) Air might be in the heater lines.
2) Blend door actuator is stuck.
I have the same issue only it's accompanied by a plastic-like squeek. Still makes the sound when the engine is off and just the key on. It's buried in there so if your going to attack it, take your time. Gotta pull the upper dash apart. Hope this helps...