12. The film projector's march
There's nothing quite like the calm hum of a running film projector. While projectors certainly aren't ancient history yet, the advent of digital video puts them square on the endangered species list. So take in that sound in all its ratty-tatty glory; it won't be long before it's little more than a memory.
13. The rotary phone rock
"Back when we were kids, junior, we had to dial phones with our cotton-pickin' fingers! Our hands got tired, sure, but we soldiered through it. Why? Because that's all we had, that's why! You silly hooligans and your fancy-schmancy cellular telemachines. Poppycock, I tell ye. Dadgummed poppycock."
(Lecture given in the year 2022 by someone who inexplicably talks like he was born in 1922)
14. The pay phone jingle
Don't tell Lois Lane, but I'd be willing to wager a quarter that most teens today have never used a pay phone. That jingling sound of your coin falling in or some change dropping back out? It's a relic of a time fading behind us.