Unfortunately it didn't fix the issue completely. It did get a lot better back when I tested, but the clatter seems to get worse as the temperatures drop. The car can be almost silent if it's plus centigrade outside but with colder temperatures and packed snow bumps it's still very audible and irritating. The only good thing is that there is no noise when driving at highway speeds, only at low speeds <50km/h.
I have an appointment booked at Tesla so among other things I'm really hoping they can find and fix it this time. I wouldn't completely rule out the steering rack as the source but there is no harshness or impacts that can be felt through the steering wheel, only noise.
I bought the STP mat from Finland during my trip there so I don't know where it can be found here. But unfortunately it's not a real solution even if it did dampen the clatter especially when it's a bit warmer outside.