Had the same problem but only on or after days I used the washing machine. Washing machine inlet valves are constructed differently from faucets and air could be sucked in and then the air bubbles rise and migrate elsewhere in the plumbing system.
Or another faucet somewhere wasn't really tight and air got sucked in from there. (It's not a good idea to really crank down faucets tight as that shortens the life of the faucet washer.)
The whole problem might not be worth worrying about but if you really want to, try turning off the shutoff valves under the sink or whatever for one particular faucet or shower or toilet for several days (don't use that fixture) and see if the problem goes away. This could help narrow down on the source of a problem.
Or another faucet somewhere wasn't really tight and air got sucked in from there. (It's not a good idea to really crank down faucets tight as that shortens the life of the faucet washer.)
The whole problem might not be worth worrying about but if you really want to, try turning off the shutoff valves under the sink or whatever for one particular faucet or shower or toilet for several days (don't use that fixture) and see if the problem goes away. This could help narrow down on the source of a problem.
