Whenever someone flushes a toilet (any of the three toilets) the pipes make a very loud piercing/shrieking/whistling noise for about 10 seconds. Whenever someone runs (usually) hot water for the first time that day from any of the four faucets, the pipes also make that horrible noise. This just started happening a few weeks ago after my dad was messing around with the water heater. I don't know what he was doing but he kept turning the water (or main water) on and off several times a day. He might have been cleaning something or doing something with the water conditioner, I don't know. But shortly after this the pipes started making the shrieking noise.
Anyone have any ideas on what the problem could be?