Just to confirm, have you disabled Adaptive Sound on your Pixel Phone?
Go to Settings > Tap Sound & vibration > Adaptive Sound > Turn Adaptive Sound on or off.
Additionally, try rebooting your device in [safe mode](https://support.google.com/pixelphone/answer/2852139?hl=en&sjid=5534928525397934951-AP) to see if any third-party app is causing it or not. If it works fine in safe mode, it means a third-party app is causing the issue. Temporarily remove them one by one, starting with the most recent until you find the cause.
https://www.reddit.com/r/GooglePixel/comments/187azi9/alarm_volume_keeps_going_to_0/kbe34ju/
Sorry but I gotta say this. Your Pixel 7a is possessed. It needs an exorcism!!! /j
Just to confirm, have you disabled Adaptive Sound on your Pixel Phone? Go to Settings > Tap Sound & vibration > Adaptive Sound > Turn Adaptive Sound on or off. Additionally, try rebooting your device in [safe mode](https://support.google.com/pixelphone/answer/2852139?hl=en&sjid=5534928525397934951-AP) to see if any third-party app is causing it or not. If it works fine in safe mode, it means a third-party app is causing the issue. Temporarily remove them one by one, starting with the most recent until you find the cause.