A couple of days ago when I turned on my PC I noticed right away that my sound was lower than normal, despite being at 100%, it was hard to hear people on Teamspeak etc.
I also noticed that it is ducking audio, across all programs. I have it disabled in sound settings when receiving a call etc, but if someone makes a loud sound in teamspeak it lowers my music volume for a second and then comes back up, if I play a game such as CS it does the same thing every time there is a loud noise.

It's as though it's trying to protect my hearing or something by not allowing anything to go above a certain volume, but there seems to be no consistency to what noise gets turned down, if someone yells in Teamspeak for example it might decide to duck the audio of the game, or a loud noise in the game might cause it to duck music/teamspeak.
I've checked all the sound settings in Windows, Skype, Teamspeak to see if any of them have any issues to no avail. I have rolled back, reinstalled and checked that my audio drivers are up to date. I am using a Sennheiser PC363D headset which has a USB sound card, so I'm not using the onboard Soundblaster drivers.

I did notice I had new Windows updates install around the time it broke, so I rolled back to before the update, however it didn't make any difference. This did happen to me once before but after about 10 PC restarts it automatically fixed itself, so I have no idea what caused or resolved it in that case.

Has anyone else experienced this or have any idea how I might be able to stop it happening?
Thanks in advance