Unfortunately, I don’t have an answer to your question but...Do you have any plans to write up your sound deadening efforts? I’m planning on doing the same thing when I finally get my materials from amazon and could use any tips and am interested in your results.
I don't mean to hijack the OP, though I hope this is helpful since it's related to the topic. Sorry I don't know the answer to your bolt torque question.
I have two 3s, one with extensive sound deadening and one with other mods, and they sound about the same. I don't have a non-modified 3 to compare to though.
When using a sound meter, the numbers jump around a bit, but both cars are fairly similar at 35mph driven on the same roads, same time of day. I'd say the car with deadening has a slightly lower overall tone, which is more pleasant, though it could be my ears tricking me.
I still need to test both cars again at 70mph, but for now, both cars are getting 64-67 dBA on the following meter (though on different days so temp and wind may have been different):
https://www.amazon.com/gp/product/B00ECCZWWI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
For the sound deadened car, I pulled all four door panels, the front carpet, and applied Dynamat-type material to reduce vibration, followed by closed cell foam and mass loaded vinyl. Though I didn't remove the front seats, I also covered under the rear floor with the dynamat, actually Noico, material and inside the roof of the trunk. Be very careful and watch videos on the rear doors, as you don't want to mess up the window regulator when getting into the inside of the door under the interior trim.
For the second car, instead of the effort above, I put the Tesla sunscreens on both roof glass pieces, and for the front one, I added some thinsulate material against the glass. The second car also has the extra door seals they sell on amazon. I did have a wind noise issue on the driver's side that I mostly fixed by adding additional "D" shaped seal under the main door seal to make it stick closer to the window. You can find those instuctions here:
Wind/road noise from doors/windows -- fix it for good
FInally, for both cars, (on 19 inch wheels), the sound deadened 3 has Pirelli Cintuado P7 Plus All Seasons at 40psi. The other one is a stealth model and has Michelin Pilot Sport 4S summer tires at 40psi. Both cars have Lloyds Luxe mats, which are plush floor mats.
Unfortunately, I don't have before and after measurements, since I didn't buy the sound meter until after I had completed the work. I've read that two other benefits to adding the sound insulation is it should help with insulating from hot/cold outdoor temps and stereo performance.
My theory is that any remaining noise is coming through the windows themselves and there's not really a solution for that. Edit: I should add that I'm overall pleased with both cars, considering they're sport sedans. In my personal opinion, changing the tires, running them at 40psi and the roof insulation made the easiest and most impact. Everyone's ears are different, though, so you might experience a bigger difference. You might find that combining the sound deadening and the roof insulation will be even better.
Even without all this hobby work, I still think they're the best cars you can buy today.
