I have a bit of a new twist on a common question here. First - I live in an approximately 30 year old house in the Chicago area. Obviously not cold here right now, but we have had a lot of rain lately (not sure that's pertinent). When I first moved in 1.5 years ago, I noticed a knocking noise in the basement ceiling whenever water was being run (hot or cold). I determined it was the 3" PVC drain pipe banging the drywall. I cut open the ceiling in that spot, and secured the pipe to the floor joists with a metal band. I shoved insulation under it to further block the noise in the basement. This worked great for the last 1.5 years.

So, starting about a week ago, it begin again... only its louder, and it seems to occur constantly rather than only when something is draining a lot of water (tho I think it is triggered by water running and may subside over time). I hear a loud knocking every 10 minutes or so... its a bit different this time in that I hear it more upstairs rather than in the basement. I suppose its possible my metal band came undone, but it seems doubtful as I secured it with multiple screws. I'm also suspicious about why I'm hearing it much louder upstairs at this point - the pipe was not anywhere near the subfloor when I secured it - it was hanging just above the basement ceiling. The noise at that time was clearly the pipe hitting the ceiling drywall.

I also want to point out that I believe this started around the same time I was doing some plumbing in the 2nd floor bathroom. I shut off the mains so that I could replace a cartridge in my bathtub fixture. Is it possible I caused some kind of airlock when I did this? Then again, this is a drainpipe we are talking about, so I don't necessarily see a correlation. I've also noticed my shower and various sinks are draining slower over the past few months. Might be various local issues, but I haven't checked into it yet (toilets seem fine). Thought I'd point this out in case debris in the main drain could be causing this noise as well.

Sorry for all the info, and any input would be appreciated.

Jeff

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Originally Posted by affeking

I have a bit of a new twist on a common question here. First - I live in an approximately 30 year old house in the Chicago area. Obviously not cold here right now, but we have had a lot of rain lately (not sure that's pertinent). When I first moved in 1.5 years ago, I noticed a knocking noise in the basement ceiling whenever water was being run (hot or cold). I determined it was the 3" PVC drain pipe banging the drywall. I cut open the ceiling in that spot, and secured the pipe to the floor joists with a metal band. I shoved insulation under it to further block the noise in the basement. This worked great for the last 1.5 years.

So, starting about a week ago, it begin again...only its louder, and it seems to occur constantly rather than only when something is draining a lot of water (tho I think it is triggered by water running and may subside over time). I hear a loud knocking every 10 minutes or so...its a bit different this time in that I hear it more upstairs rather than in the basement. I suppose its possible my metal band came undone, but it seems doubtful as I secured it with multiple screws. I'm also suspicious about why I'm hearing it much louder upstairs at this point - the pipe was not anywhere near the subfloor when I secured it - it was hanging just above the basement ceiling. The noise at that time was clearly the pipe hitting the ceiling drywall.

I also want to point out that I believe this started around the same time I was doing some plumbing in the 2nd floor bathroom. I shut off the mains so that I could replace a cartridge in my bathtub fixture. Is it possible I caused some kind of airlock when I did this? Then again, this is a drainpipe we are talking about, so I don't necessarily see a correlation. I've also noticed my shower and various sinks are draining slower over the past few months. Might be various local issues, but I haven't checked into it yet (toilets seem fine). Thought I'd point this out in case debris in the main drain could be causing this noise as well.

Sorry for all the info, and any input would be appreciated.

Jeff

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This is a long shot, but I'm sure all the suggestions will help..

The pipes that lead to your taps should run past the actual pipe connections to the faucet.
This is hard to explain... if the pipes are coming from the floor to your bathroom taps the pipe should go past the taps by about 3 inches and then be capped at the top. I have experienced pipes that are ran direct and when turning on the water it causes the pipes to bounce off the wall. Running the pipe past the connection and capping it reduces this pressure.
I know this is very confusing and may not be the solution to such an issue that could have so many variables involved. Just thought I would pass off my experiences.

Wade is referring to air chambers that we install on all lavatory and kitchen supplies. These act as shock absorbers to hold down water hammer. It has nothing to do with drainage. As for generating a airlock I don't think so. Air locks can be dealt with by opening the uppermost faucet and bleeding the line. Could this be a vent stack that's expanding and contracting with the summer heat? Regards, Tom

Thanks to both of you for the input.

I'm not sure about the vent stack. It hasn't been particularly hot, so I'd be surprised. Unless the humidity might have caused the issue... In any case, what's the best way to confirm that is the cause? I'm not hearing the noise upstairs, so I'm doubtful that's it. Could this cause knocking in the basement but not on the 2nd floor and attic?

Another thing I forgot to mention... the last time this happened, applying pressure to the basement ceiling just below the pipe made a noise. Now it doesn't, but stepping on the floor upstairs seems to. Again, that seems very odd since the pipe is not close to the subfloor.

If you couldn't tell, I really don't want to rip up my freshly painted ceiling again :)

Thanks,
Jeff