Do you have a pressure reduction valve in the house? These typicallyhave a check valve in them. Also, so water meters have them, and some municipalities use them as well. Any of these will create a closed system in your house - water will come in, but not out. Now, that protects the rest of the neighborhood from potential contamination that might creep infrom your house, but it creates its own problems within yours. When the hot water heater heats the incoming cold water, the water expands. Sometimes, this increase in pressure hitting up on the check valve, if it leaks a little, will make some noise as it leaks back through that check valve. Now, this may not be what is happening at all.
At a plumbing supply house, and maybe a big box store, you can buy a pressure gauge that will screw onto a hose bib. A place in the house that would work if you don't want to go out in the cold would be the washing machine connection. Check your pressure. Take a bath, check it again. Then, watch it and see if it goes up as the hot water heater recovers. If the sound happens when the hot water heater is running, thatmay be your problem. If it isn't, somebody else will probably have some ideas.
