Upstairs toilet causing concerning noises when flushed

[centex_built]

I'm in a rather newly constructed (2006) Centex house. When the upstairs toilet is flushed, then from downstairs it sounds like a "crappy" waterfall is splattering about from within the walls. Obviously this is cause for great concern. I really can care less about the noise (see a post from Primer about noise solutions). I'm concerned with the nightmarish possibility that the drainage pipe under the toilet has come loose (OR never installed from the get-go by Centex... which would not be surprising by the way given their lack of quality in construction) and sewage is just falling freely and collecting inside the walls.

A few observations:
- The upstairs toilet operates fine. water level seems steady & flush is fine.
- No signs of water damage to the adjacent walls of upstairs toilet
- cockroaches seem to be found occasionally in stairwell (which shares a wall with the upstairs toilet).
- Sometimes (rarely) when the central air kicks on a foul/decay smell exists for a few minutes mostly in the area that shares wall to upstairs toilet.
- There seems to be a foil drain smell occasionally in the bedroom where the upstairs toilet is. Not sure if this is from toilet or from sink, tub, shower drains.

Questions:
- Is there a way to determine if the drainage pipe is disconnected under the toilet? Possibly from the water level in the toilet?
- Any pressure test that can be done to determine if there is a pipe disconnect/leak?

Kinda wish I had a snake camera to feed into the wall so i can take a peak...

Thanks in advance!

 

[phishfood]

If the home was built in 06, an unconnected drainage pipe would have caused massive damage by now.

A plumber or drain cleaner with a sewer camera could verify whether or not the pipe is connected, but without major signs of water damage, I wouldn't waste time on that.

The smell is another issue altogether. It is possible that a vent pipe is compromised in some way, and that is what is causing the smell. A smoke test is the best way to check for that, but again, you will need a plumber who has the equipment and know how to perform such a test.