I have my front yard sprinklers turn on at 5:30 and 6:00 am every morning. When they shut off, I hear a water gurgling/gub, gub sound in my master bedroom ceiling/wall which is on the second floor. Doesn't happen with the backyard sprinklers.

When I get up at 7 am, I also notice that there is no water coming out of my hot water faucets (in none of the faucets in the house first and second floor) altho the cold water runs fine out of the cold water side.

After a few hours, the hot water is running out of all the faucets just fine.

What on earth is going on?