needing advice - noisy pipe

[momof5boys]

We moved into a new home 10 months ago and I am now noticing a knocking in the wall whenever our washing machine shuts off the cold water. The builder just came in to install a couple of extra water hammer arrestors but the noise is still there. What do you think - maybe a water pipe that hasn't been clamped properly? Would this cause problems down the road? The basement is finished so it would mean cutting through gyproc to get at it.

[Natalka]

Wow, that shouldn't be happening in a new build.

I'm no plumber, but maybe it's the valve - pressure needs to be reduced
http://home.howstuffworks.com/question89.htm

[momof5boys]

Interestingly, after one load of laundry, the knocking is gone. Those hammer arresters must be doing their job. Hopefully the wall stays quiet now