The SD card was fine, but while adding more songs (mp3) the others started having those weird short bursts of sounds. Sometimes short parts (0.2 s) were just missing. The more I added, the more those sounds appeared throughout the songs. They were still at the same place though. After I removed some songs I didn't like, the other songs seemed to get rid of some of the errors.
This is definitely not a player issue. I tried copying the damaged files onto my pc and those errors remained there.
Also the pictures I had stored (maybe jpeg?) went a bit corrupt. The top half would mostly be fine, but from a certain point the whole bottom part was overlapped by a certain color.
The card in question is SanDisk 16GB, at least I think. May check later if it's important. Android 7.0, phone is Huawei p9 lite mini.