I have the same problem (Blu Studio 5.0C HD). My phone is constantly unmounting and asking to remount the SD card, with a notification chime every time.
(This phone chimes at me so much I often miss texts, as I'm so used to ignoring it for notifying me of nothing so often. I went through and turned off every notification I could find. It would be so nice is there was a general 'turn off all notifications' except for text.)
I tried another SD card; same thing. I'm not going to buy another just to find out it's doing the same thing, as I suspect it will.
It has done it twice while I wrote this.