Loud Bangs Coming from PVC waste pipe and Hot Water Copper Line
A year ago I had a crack and leak in our PVC waste pipe just behind our family room wall close to the first story floor. The plumber opened up the drywall and cut out the cracked portion (2 feet) which exended from just behind the family room wall down to the basement and replaced it with a new section. A few months later when it got colder I noticed that 9 times out of 10 when you flush the toilet in either bathroom upstairs I hear 2 or 3 loud bangs about 4 seconds after the toilet is flushed. The banging is coming from behind the wall right next to the PVC waste pipe just below the 2nd story subfloor. The banging is much more frequent in the colder weather. I don't believe there is a water hammer problem because I didn't notice a problem until a month or so after the plummer had replaced the section in the PVC pipe and we have lived in the house 18 years.
A few months later after I noticed the problem with the toilet flushing I began to notice that every time a hot shower is taken in either upstairs bathroom about 5 minutes later I hear a similar bang. The banging occurs one time every two minutes and this goes on for an hour after the hot shower. It is only one bang every two minutes. The sound is coming from a location next to the where I hear the toilet bang. The hot water copper pipe is located behind the wall where the sound comes from and just a foot to the right off the PVC waste pipe. It sounds like it is coming from just below the 2nd story subfloor. I am familiar with thermal expansion and the pipe is becoming longer and thicker as it heats up but it is very strange to me that the bang occurs just once every two minutes and this goes on for an hour. I also experience the same sound in the same location around 9 am every morning for a hour and then sometimes around 9pm at night for an hour or so. This has been going on every day for over a year and I would like to resolve the problem. If somebody can give me some helpful advice I would really appreciate it. Thank you!