First of all, it's key to define the difference between a rattle, and a rough coaster. A rattle is just a noise caused by vibration... Depending on their tolerance, that vibration can induce headaches, amongst other things, in some people, affecting their enjoyment of the ride. A rough coaster is just rough, something that aggressively throws your body around in ways that can hurt parts of your body.
Rides like Ride to Happiness, Voltron, Taron, Hyperion and so on, all have a rattle. Old woodies like Grand National, Bandit, Loup Garou or some old Vekomas like SLCs and boomerangs are rough, in that they can cause some parts of your body to bang violently against parts of the train or restraint.
There is a bit of a grey area between a very very strong rattle, that causes constant strong vibrations, for example the type that has your head bouncing against a restraint, and roughness. But at that point I would say that rattle has gone beyond a rattle, and the coaster is just plain rough.
When talking about a rattle, particularly on newer rides, we're usually talking about mild to moderate vibrations and sounds. We mention them, even when they don't impact our own enjoyment at all, simply to inform. Because other people cannot tolerate even these mild vibrations. But also as something to watch in the future, in case it gets worse.
For me, I think I have a fairly high tolerance to rattles, and even enjoy some very rough coasters, as a bit of silly fun. That's never going to mean I do not notice the rattle, or roughness. It's there, I just don't care.
However, the frequency of a 'constant rattle' seems to be important for me. For example, Saw. I have ridden, and enjoyed, rides much rougher, rides with a stronger rattle, but there's just something about the frequency of Saw's rattle that seems to induce an instant headache for me, even when it doesn't affect people I travel with who are usually more susceptible to rattles and roughness. I don't think Saw's rattle is that strong, I've certainly been fine with rattles I'd consider to be stronger in the past. So I've come to the conclusion that there's something weird going on with the frequency and my body's reaction to that specific frequency... To make this even weirder, I've discovered over the years that downing a couple of pints of water in the 30 minutes before riding Saw actually helps. I am not somebody who doesn't drink enough, I drink plenty, and this is the only coaster that I do this for...
I know weird right? No idea if frequency and some kind of resonance is actually what's at play, maybe I'm talking nonsense, but either way, I still cannot ride Saw more than once or twice, whilst I'll happily enjoy rougher and more rattly rides over and over.