I've been noticing a consistent knocking/tapping noise when cold water is running in my house. It gets louder with more volume. It stops when the water is turned off. Not sure how long it's been happening. It appears to be coming from the vicinity of this part. Can anyone tell me what this part is and if there is a valve or something in it that could make this noise? If so should it be replaced? Since the whole pipe is vibrating it's difficult to pinpoint. This is the only part I can find on the water line between the shutoff and the rest of the house. However, given that this was buried in the wall, it's possible there could be something else.
That is nothing. It's just a tee fitting with a short piece of pipe that is capped off. That shouldn't make any sounds or cause any issue. As for why it is there - no telling. Installer could have ran out of couplings and had a tee handy, or read a diagram wrong and thought there needed to be a tap there.