AirPods 3 volume fluctuates unexpectedly

Random loud/quiet swings on AirPods (3rd generation) usually come from a software setting, not the AirPods themselves. Worth checking on the iPhone: Settings > Music > Sound Check (it evens out loudness between songs and can cause jumps), Settings > Sounds & Haptics > Headphone Safety > Reduce Loud Sounds, and any Personalized Volume toggle in the Sound settings, which adjusts volume automatically based on your environment.

Also try a quick reset: put both AirPods in the case for 30 seconds, then restart your iPhone and reconnect. If it persists, Apple's steps for restarting and resetting are here: https://support.apple.com/guide/airpods/restart-unpair-or-reset-airpods-iph561965261/web

Does it happen with every app, or only with one (Spotify, YouTube, calls)? Also, does it happen on another device?

I have this problem also. All setting are off. I’ve reset the airpods. I am also using in a quiet house—no loud noises and still volume fluctuations. I notice if I shake my head it usually fixes the issue. This is happening with two different airpods and 2 different apps, that I’ve noticed so far.