voltage drop?

so i have the toyota corolla 2020 and it comes with 100 amp stock alternator. my audio system total ia 1000 watt and my amps are class d efficenent. i installed 2 days ago a stinger voltemter recommended by someone in here. and i did install it on the amp since the connection was there and it was easy. anyway my voltage on really loud bass drops sometimes which is very rarely to happen it drops from 13.4 to 12.8 or 12.6 and then goes back up very quickly. i dont wanna ruin my new car because im still financing it. if it comes to it i would remove my system then break the car. usually if im not that loud it doesnt happen