Rumbling When Toilet Flushed

[jpetroz]

My wife and I just moved into a newly built house about 6 months ago. This problem has existed from the day we moved in. Whenever solid waste or even toilet paper alone is flushed down the toilet in the master bath (on the second floor), there is a loud rumbling sound heard several seconds later in pipes that seem to be running inside of a first floor wall. It sounds like thunder and only lasts a few seconds. To me, it sounds as if this sound is created as the waste passes down through the pipes. I am not a plumber, but do have some basic knowledge. I am sure that this is not a problem with the ballcock or with the supply lines, or with water hammer. Something is causing this rumbling sound as the water/waste moves down through the pipes. There is another toilet in a another bathroom on the second floor, but this one does not cause the same rumbling sound when flushed. Any explanation for this sound and possible fixes would be much appreciated. Thanks in advance

[krow]

Just a shot in the dark here.

Is it possible the verticle stack is not fastened properly? So that when the large amount of water hits an offset in the wall or floor/ceiling, it could be moving.

Another possibility, sometimes, if there is an AVV in the line, it may flutter when discharging large amounts of water (Its probably unlikely)