Every time one of our toilets if flushed, the water line makes a knocking noise.  It never use to do that until we replaced the flapper and flushing valve.  Does anyone know what this might be?  It's very loud! ::)

Most of the time knocking is caused by long unsupported lengths of pipe. The knocking happens when water is turned of quickly and the preasure is built back up in the pipe. I would think it is the new valve you put in the toilet. Do you know if the shut off valve was fully opened before you closed it to do the repair. The first thing I would do is play with the preasure going to the valve. Try partualy closing the shut off. You may have to make different adjustments to eliminate the knock and still have the tank refill in a reasonable amount of time. The reduced flow will increase the preasure in the pipe and reduce the preasure on the valve. Hope it helps!

Sounds like you may have water hammer. Back in the 60's we were required to to put shock absorbers,(air chambers) on all bath lavatorys and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will begain to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back. You have just recharged your air chambers. Good luck , Tom

I have a similar problem, but without the 'air chambers' or 'angle stops'. Can't figure out what is being referred to in the above solution. Newer home producing 'clunking' of water line behind fridge, every time the sink/toilet is used. The line is expanding and collapsing extremely so as to bang the wall and fridge. Tried clearing out the line with the above steps and it seemed to work for a few hours, but the problem has since returned, although slightly more quiet.
Please help! This is starting to drive me insane! It must be on some list as a sick form of torture.

Thanks in advance,
Deb