I have a sprinkler problem in the front yard that has made it necessary to turn off the supply to the house. SInce I did that, the gas water heater has started t make squeaking noises.

What, if anything should I do?

I would say that the noise you hear from the water heater is the water in the very bottom of the heater, under a layer of sand and calcium that builds up, the water heats and small bubbles work their way through the build up and make that noise. Nothing to worry about as long as the pressure does not get too high in the heater, you can make sure it doesn't by opening the hot water valve in the bath tub.