Random "Device Connected" beep on MacBook Pro
I have recently started noticing random "Device Connected" beeps from my MacBook Pro (like when you connect your iPhone or iPad) when nothing has been connected via USB at all. Does anyone know what this is? It's driving me nuts and can't find any answers on the online forums ...
MacBook Pro (13-inch Mid 2012), OS X Yosemite (10.10.2)