About a month ago the flush of a toilet caused a very loud fog horn sound with lots of vibrations through the pipes (through out entire house? Not sure). I was hoping it was a strange fluke. Well, it turns out ALL the toilets will do this, upstairs and downstairs, about half the time they are flushed. The noise happens near the end of the flush, when the tank is almost full again. Since this started at the same time for every toilet I am guessing it's not a simple fix inside the toilet (could all 3 develop the same problem at the same time? ). Any ideas as to what is going on and how I can fix it. The noise always wakes my kids up during naps/nighttime.

Do you have a PRV (pressure regulating valve)?

What ballcocks are in your toilets? Let me know, Tom

hkstroud, I don't think there is a pressure regulating valve, not that I see anyway. Tom (speedball1) they are the second kind with the chain.

Next time the noise occurs, very quickly open a cold water faucet completely. See if it makes the noise stop.

Will do. The noise only occurs for a few seconds sometimes, but I will try.

Third flush was a charm. Yes, turning on the cold water stopped the noise right away.