Designing Kitchens and Bathrooms - Noisy toilet

We have a timberframe home and the upstairs floors are car decking, about 1-inch thick fir. The toilet upstairs is mounted directly to the planks and when anyone uses the toilet, you can hear the personal activity downstairs. A bit embarrassing! The house was built in 1984 and has old linoleum which we plan to pull up. Any suggestions on soundproofing the floor?

Insulate around the toilet drain.

the problem with that is the drain is through the wall - this toilet has a rear outlet, not through the floor as the floor itself is simply 1-inch cardecking (this is a timberframe house) and there is no insulation between the upstairs floor and the downstairs ceiling.

Are the noises you hear from the flushing of the toilet, or the activities that take place prior to flushing? Trying to determine what needs to be insulated, and your post is somewhat vague.

the noises are that I want to dampen are as you say are the activities that take place prior to flushing! It sounds like a waterfall downstairs

I am leaning toward the floor as the culprit, but may not be at the toilet itself. There will be large cutouts in the floor for Tub and Shower drains as well as access points for faucet and toilet supply lines. The biggest opening will be for the tub drain. I assume that the ceiling (as viewed from below) is a T&G board and not sheetrock.

I think that you need to pinpoint where the noise is loudest first. Tag Team with someone who can be in the bathroom while you are on a ladder listening downstairs. Have them pour water into the toilet to simulate the sounds while you shift around below to find where the sound in loudest.

If it is from the tub cut out, you will need to gain access from an adjacent room to stuff insulation under and around the tub and drain assembly. The tub may be acting as a resonator to increase the sound.

If it is the floor, try putting several layers of blankets down to see if you can insulate and quiet the noise (prior to installing expensive flooring). Again, do the tag team thing.

If it is the toilet drain pipe, you will have to access by getting into the wall cavity to stuff insulation around the pipe.

Check at each water supply line to see if there is an exceptionally large hole that can be stuffed with insulation.

If you have wood floors and wood ceilings (from below) you have made basically a resonator box. Same as if you look at a guitar, a single string plucked by itself makes little noise, but pluck that same string over an open box (ie the guitar) and it makes a loud noise.

Either way, we need to get some sound insulation in your house, but lets find the source first.