How to circumvent "System-UI has stopped" when I turn up the sound volume?

[AC Question]

I have a Motorola Moto G (3rd generation) and I have the problem since I have introduced a microSD (SanDisk Ultra Android microSDXC 128GB). Only when I listen to music or other media via headphodes (without headphones, everything works fine), I cannot turn up the volume to full level anymore. At a certain level, the following message would come up: "System-UI has stopped" and the phone goes into key lock.
How can I circumvent this?
I would be very grateful for advice. Many thanks!