No reply since August?
I'm also experiencing this same problem. Never had this issue previously, just started happening recently.
Running as Admin
Changed the hotkey
Changed the hotkey setting from 'Default' to 'Mouse & Keyboard Only' (my only two options)
Changed the source from best to direct sound
Updated drivers
Tried running with different compatibility
Reinstalled the client multiple times (completely wiping all files)
I did notice that when this happens, TS3 stop recognizing that a hotkey had even been set and will not allow you to set a new one with the keyboard nor the mouse (ding, ding.. like they aren't even plugged in)