Default SD Card Help

Hi guys,
I need your help becasue this looks very weird to me. This is my situation: I have a I-9500 (Stock ROM 4.3, no root) with Kingston SD Card 16 GB Class 4. On the SD I keep only my music in one folder, nothing else. Also because I have a lot of music, more than 14 GB, the card is almost full. Sometimes the back of the phone where the SD slot is, becomes to warm up a lot and battery starts to drain very fast. It has happened to me in different situations (and also prior to update to 4.3): once I was indeed listening to music, so using the card, but another time I was taking photos and watching a video saved on the phone. Like I said, I save everything (ecxept music) on the phone.
To solve, I have to either take the card out or format it in the phone. Once I do either of them, the phone cools off and battery drain goes back to normal. Once it even went into a boot loop, before I realized I had to take the card out.
We have 3 options:
1. it's the phone
2. it is something in my music folder (I have photos of the cover albums, which shows up in Gallery... could this be the cause?)
2. it is the SD card brand, capacity, class... I read on many forums about problems with certain brands, even though, if I recall correctly, it affected mostly 64 GB cards...

I want to add I have a Note I-5100 with a Sandisk SD 32GB Class 4 and never had any problem, I want to swap the two, but I know that even if something happens, it will not be immediate and I prefer to have the big one in the note. If I knew changing SD would solve it, I would go for it immediately, but I would like to know what you think first. I have also read Samsung SD cards perform better in Samsung phones. Is this true?
Thank you very much for your help!
I just noticed that many album folders have a file named n7p_art, which is created by the music software (I use stock Samsung Music Player). could this be the cause?