air in lines

Whenever our electricity goes off (storm, power outage,etc.)it sounds as if there is water \\\"swooshing\\\" around in the pipes of our laundry room. After this happens all the downstairs faucets have air in them and come on with explosive force. We recently had our AC/heater units replaced & our water heater had to be turned off during their work. My husband also recently replaced a shower head in our downstairs bath. Could either of these recent events be causing this? We also have a slightly musty odor coming in through the vents of our house occasionally. We have a crawl-space underneath. I fear we have a leak of some sort causing all of this. Any ideas? Am wondering if to call plumber or AC company. Thanks!