If excess dissolved air becoming insoluble when cold water is warmed by indoor piping is the reason, you (generic "you", not "you you") can actually watch the bubble front rise from the bottom of a glass over time, leaving clear water below and cloudy water above. It's some super-cool physics IMO. It also lets you (again generic "you", not "you you") see whether it's something other than air bubbles coming out of solution.