3DS popping problem, but I'm sure it's not the speakers

A long while ago my brother's (first model) 3DS system's top screen went out, and ended up with the problem that about 80% of the time it would turn on, 2-3 seconds would pass and then the system shut off with a pop. We were recently able to get a system transfer done and put the data onto a New 3DS (3DS 2015) system. The New 3DS happened to start up fine after the transfer, but a reboot showed it had the same problem the first 3DS did, and now the 3DS works fine without any popping. I've seen the "micro tear in the speaker cables," but this seems to be a system data error, as the system transfer got rid of the problem on the first 3DS, but sent it onto the New 3DS, and removing the SD card on the first system (before the transfer) did not solve the problem. This is seriously frustrating for him because he went about 6 months without being able to do anything on his 3DS (hence, top screen,) and now that he got his new system and watched it break before him.

We have no idea what is going on here, but maybe you know...