I think the 'air' in the pipes that you're referring to is related to small pipe extenders that 'cushion' against "water hammer". They're about 4-6" long and usually a size larger than the household pipe, to hold a bit more air. These are often placed by valves that suddenly shut off water (such as d/w, washer). Other than that, air in pipes probably isn't much good. (You may not have the air cushions...I don't think my house does.)
Another cause can be that pipes aren't anchored properly. This was happening in my ice maker line--which used to be just a long 3/8" copper tube without any anchors. When you shut off the kitchen faucet suddenly, it would clank. Pipes do need to be anchored properly. Typically copper anchors are used (for copper pipe)--to protect against long-term deterioration caused by the electric action between different metals--but I've used plastic ones and they work quite well.
k2 in CO