I am using the Belkin Thunderbolt 2 Express HD Dock to connect an external monitor, speakers, and a powered USB hub to my MBP 13" mid-2012 running OS X 10.11.3 (El Capitan). Over the last week, I've noticed that my external HD will disconnect and an error stating that the drive wasn't ejected correctly will pop up. I've also noticed that the speakers will disconnect...sending whatever I'm listening to through the built-in MBP speakers. To make it even more confusing is that the external monitor is not affected. All of the external peripherals are utilizing their own power source. Dock: Belkin Thunderbolt 2 Express Dock USB hub: Sentry USB 3.0 HUB + CHARGER External speakers: Harman Kardon Soundsticks III 2.1 Channel Multimedia w/ Subwoofer External monitor: HP w1907 The only experiment that I'm able to do with my limited knowledge base of computers is to hook my HD directly into my MBP using one of the USB ports. Since connecting the HD directly into my MBP, I haven't seen the error pop-up. Any ideas as to what the issue is and how to resolve it? I don't have the technical knowledge base to run diagnosis or to deep dive...so any help to figure this out is greatly appreciated.