We have a chugging noise when we use the water in certain areas of our home. It sounds exactly like a train leaving the station with an accompanying squeak in time to the chugs. It only happens when we flush the toilet in the main floor bath, the appliances in the main floor laundry and in one of the upstairs showers. We have drained the system and it goes away for a while but always comes back sometimes within days, other times it lasts longer. Any suggestions?