His Galaxy Buds+ (left side) are quieter.

Hi, I found the problem with mine. I had the same issue, and you can actually fix it, but it voids the warranty. To do this, you need to remove the rubber adapter that goes in the ear, and underneath there's a metal plate you have to take off using either the tip of a knife or a very, very small flat screwdriver. Once that's done, you'll find a filter underneath that is very dirty; you remove it, reassemble everything, and that's it. Don't hesitate to let me know if you try.