"Makes me wonder what exactly causes the difference—is it just the internal mechanics, or maybe something to do with how the water moves through the pipes?"
I had a similar experience when we redid our guest bathroom last year. The first water-saving toilet we installed downstairs was whisper quiet, so I figured we'd just grab another one from the same brand for upstairs. Nope...the second one sounds like a mini waterfall every flush. When I asked our plumber about it, he mentioned that noise can depend on a bunch of things—internal valve design, flush mechanism, even how smoothly water flows through your pipes. He also pointed out that if your plumbing setup has sharp bends or narrow pipes, it can amplify noise. We ended up adding some insulation around the pipe behind the wall and it actually helped tone down the sound quite a bit. Might be worth looking into if it's bothering you enough to consider tweaking things behind the scenes.
Had to chuckle reading this...I've installed plenty of these water-saving toilets, and yeah, the noise difference can be wild. Internal mechanics definitely play a big role—some brands have quieter flush valves or better-designed traps. But honestly, plumbing layout is the sneaky culprit most of the time. If your pipes have tight bends or narrow sections, you're basically creating a mini water slide behind your walls. Insulation helps, like you mentioned, but sometimes swapping out fittings for smoother curves can quiet things down even more. At the end of the day though, if it's flushing properly and saving water, I'd probably just embrace the waterfall soundtrack and call it ambiance...
"...sometimes swapping out fittings for smoother curves can quiet things down even more."
Totally agree with this point—it's often overlooked. I recently helped a friend troubleshoot his noisy water-saving toilet, and the plumbing was a maze of sharp elbows and tight bends behind the drywall. We took the cautious route, carefully opening up the wall (after shutting off water and double-checking the pipes weren't pressurized, of course). Replacing those sharp bends with gentler curves made a noticeable difference.
Also, don't underestimate pipe insulation. It's cheap, easy to install, and can dampen that 'waterfall' effect noticeably. Sure, some noise is inevitable, but personally I'd rather not have my guests feeling like they're at Niagara Falls every time they flush...
"Replacing those sharp bends with gentler curves made a noticeable difference."
I get where you're coming from, but honestly, if I have to start busting open walls to make a toilet quieter, I'm out. I'd rather deal with the occasional Niagara soundtrack than remodel half my bathroom...
Haha, I totally get your point—no one wants to turn a simple toilet upgrade into a full-blown bathroom renovation. But you're right about the gentler curves:
"Replacing those sharp bends with gentler curves made a noticeable difference."
From my experience, smoother pipe bends do help reduce noise and even prevent clogs, since water flows more naturally. But honestly, unless you're already planning to open up walls for another reason (like fixing a leak or updating plumbing), it's probably not worth the hassle just for noise reduction. A simpler fix might be to look into insulated pipes or even just adding some soundproofing material behind the drywall. I've seen folks get pretty creative with foam insulation or acoustic panels—way less invasive and still effective. Plus, you won't have to explain to your family why the bathroom looks like a construction zone for weeks...
