Volvo: Vacuum leak, vacuum leak, vacuum lines

Question
Sorry Ray Jeff again, let me clarify something. Fan out-put increases when I let off the accelerator and decreases when I step on the gas. The "sound" occurs when I take my foot off the gas. Almost sounds like it is under the dash but not sure. Thanks again

Answer
Jeff,
Yes there are a few vacuum lines under the dash. It is now time to figure out what side and what needs to be removed to help find the leak. Also if you can not find the leak under the dash noise travels all under the dash from the engine area, so it could be a leak under the hood also. Get help from someone to drive the car while you listen to identify the leaking area.