In a piano room the audience hears the building. A singer takes a ballad down to a whisper, the room drops with them, and every mechanical noise in the place suddenly has a solo. The air handler gets blamed first and the ice machine second. The plumbing usually goes unnamed, even on the nights when it is the thing making the sound.
The noises are specific enough to identify from a seat. A single bang in the ceiling when the ice machine or the glass washer shuts its valve is water hammer, the pressure wave that follows a fast-closing solenoid. A steady hiss behind the wall near the stage is often a fill valve that no longer seats. Knocking that travels along a run usually means pipe that is not strapped tightly enough to stay put when pressure changes. On a live recording all three arrive as noise floor that no amount of mixing will remove.
Restrooms are the other offender and the harder one to schedule around, because in a cabaret room they sit close to the audience and get used hardest between numbers. A fill valve that runs on and off all evening is audible through a shared wall, and a flush during a quiet passage carries further than anyone believes until they hear a recording of it. Rooms built for volume rather than for whisper-quiet ballads rarely accounted for that, so the mitigation ends up being maintenance: valves that seat properly, supply lines that are not resonating against a stud, and pressure that is not fighting the fixtures.
None of that is an acoustic problem, which is good news, because acoustic problems are expensive. Arrestors, tighter supports, a worn valve replaced, house pressure brought back into range: those are plumbing repairs at plumbing prices. The catch is that a room open seven nights a week has no dark day to hand over, so the work happens in the morning and has to be booked in advance.
That is the case for a number on file rather than a search at nine at night. A.A. Cassaro Plumbing, which lists emergency calls alongside everyday repair work, takes on residential and commercial properties around Las Vegas. Anyone running a room where sound carries may find that worth keeping next to the piano tuner's contact details.
Try this at the next soundcheck. Clear the room, kill the music, and stand still for thirty seconds with a notepad. Write down each sound and where you were standing when you heard it, because that list is what a contractor can actually work from, and it beats telling someone the room makes a noise sometimes.