All ones have the same issue. Only the first one wich i used few days didn‘t make noises, so i think i brick it..
The SD Card works fine.. i tested it with sc card reader (see sd card test thread)
I use two different sd cards on DFplayer and both makes no difference.
At last i tested it again with 0001.mp3 in mp3 folder and i was able to playing this song with IO2 Switch and sometimes it was possible to read Serial Interface with arduino. Arduino detects 6 files but only one mp3 file exists (maybe the system information folder will be the reason for this).
But after each play finished it makes the buzz noise. sounds like the same if you have a bad tv antenna without signal.
I orded new df players and 3.3v power transformers. I will check it out next week.