I have lived in New England or New York my whole life. No modern vehicle (post, say, 1990) of mine has rusted. They figured that out years ago. That said, I still use a undercarriage pressure washer attachment to power off the salt periodically in the winter. Though that's a recent purchase, so...
It is likely the glass. You can either put a piece of tape along the inside of the top of the tailgate where the rubber on the glass hits, or apply some silicone grease to the rubber seal. I used Shin-Etsu and it's silent now.
Modern performance cars have "cold air intakes" as stock, since they pull air from the grille, not the engine compartment. In fact, a lot of the intakes I've looked at for previous cars are worse for air temp, not better. Best you can do is improve flow. And if you ever plan to take your Bronco...
My guess is that the app shows the last reading, and when you get in and start the Bronco, the pressure will be lower as the tires are cold, hence the lower reading on the screen. What happens if you check the app immediately after driving? Does it match the?
I solved that issue by buying the Bronco for my wife. That let's me keep my toy, a Lotus Evora GT.
To be fair, my wife has always wanted a Bronco, so she was 100% on board with the plan.
Realizing my prior post was not especially helpful... No experience with Memphis speakers. But if all you're upgrading is the speakers, no reason to go crazy. Any decent speaker will be fine. I went with Kicker CS speakers and I think they outperform the amp.