You should hear some of the 'power flush' units on the market.

They use a tank (often flexible in some way) to store water under line pressure, and then release it to scour the bowl with reduced water volume.

You may be able to reduce the flush volume and still get an adequate flush based on the higher velocity obtained with the higher tank.

Yes, less water may help, given it's a decent fall. What I'd do, though, is insulate the tank if it doesn't have the foam lining already (to prevent condensation) - it may help.

If it's just water noise in the bowl...well, as they say, "another first world problem."

In the scheme of things, it's not the end of the world.

Power flush is loud. We tell visitors to stand before flushing to keep their insides in.

IIRC, when the first flush toilet was put into the Queen's castle, it scared her (QE the first) so much she refused to use it.

Weed: I can believe it. DH is ordering some new guts for it to see if that helps the noise. I said we should just live with the noise and give the toilet an appropriate name. He thought "noisy f*&%^$" was appropriate. Sorry but that's what he's calling it, lol.
raven: I'll have to remember to warn visitors, too. Maybe a bowl of complementary earplugs set out somewhere?

What gets me the most is on the website, they specifically say "quiet". What a load of bollocks.

bus_driver: you're right, of course. We are making peace with it. It is very beautiful and we own it and it's installed. Just the initial shock was a bit off-putting. Love your story about the indoor toilet... it is all in the point of view, isn't it?