What is Considered "Normal" Cabin Noise?
 

I seem to have forgotten how loud the cabin can be on my BRZ after 3 weeks of not driving it. Car barely has 27K miles in it. 2018. But I feel like either the tires got louder because I can hear an osculating noise when going 65mph+ and reducing speed or maybe it could be something else. I know these cars are not known for being quiet, but it made me wonder if its maybe a sound that I had gotten used to, or if its something I should be taking a look at. I also know that the OEM tires aren't the quietest ones.

To add some perspective, I've been driving around in a 2019 Mazda 3. Which is absolutely quiet. Mazda spared no expense with the sound deafening materials.

Yes, the Twins are loud, especially at highway speeds. A lot of noise is tire noise which greatly depends on the type and age of the pavement - concrete is very loud, fresh asphalt is pretty quite, but nothing like even your average commuter car.
Definitely some noises might indicate a problem, but for those usually come with more years and mileage than what you probably have on your 18.

I've been driving around the last couple days with nothing in the back seat area with the fuel tank cover off and I can tell you these cars make a lot of strange noises. The rear end alone is crazy noisy.

I feel like this is a normal noise, but I guess it just caught off guard after I've been driving such a quiet ride. Could be the tires about to reach their end, they have a tiny left before hitting the wear mark.

I was also so wary of any noises because I had to bring the car to work to get the wheel switched at a near shop. Didn't put the donut on fearing I could strip the lug nuts.

One back road I use frequently has a section that makes my car hum a particular frequency.
I was wondering if something was falling off.
It was freshly paved not long ago and I think the support vehicles they ran over it shortly after rolling it flat left some non-visible tread impressions.
Don't get the same vibes anywhere else.

I also get a lot of wind noise leaking around the vertical seal of the aft-most driver door glass. That drives me nuts...

I folded down my back seats and yea, there's a lot of ear end noise.

I reckon the right kind of new tires would make a difference - ;)

Check your wheel weights for oscillation issues, may have lost a couple. Or change the road, I've had a couple stretches of visually good looking road make me think I had something wrong with my car more than once.

But you lowered that CoG of your 16 lb rear seat panel by inches. Win! There's so much going on with the rear IRS it can't help but be noisy. Look at all those bushings.

Looks like Im due to a visit at Costco.

Ive been trying to narrow down a thump/clunk/rattle noise over harsh roads so I removed everything from the trunk including spare kit and drove with the seats down. WOW, its noisy back there, and I could hear the thump/clunk even more. hoping its a bushing and not my coilovers that are done (b14), if they are ill be looking for used Performance Pack suspension, hoping they will be softer for NYC streets.

I observed that on low speeds, say below 60 km/h, most noise comes from the engine (and the "sound tube"), paired with some rattles from the suspension. Still, you can comfortably chat with your passenger.

Between 60 km/h and 150 km/h, road surface comes into play. On good roads, you mostly hear the tires, on bad roads you get a cacophony of tires, clicks, rattles and the occasional clunk. Still, the overall volume still allows you to talk to your passenger.

Above 150km/h, the wind noise increases dramatically. I'd say that above 200km/h (yay Germany), you will have to raise your voice considerably to be understood on the passenger seat.