The X31's are outstanding there is no denying that. The sound quality you get from them is perfect, like every other headset there is a slight hum when there is no sound but this is a minute problem so there is no harm there.
The main problem with these is that they are wireless and share the same frequency as many other electronics, so if you are planning on using these in a small room with a number of other electronic equipment then they wont work. There is a problem with the receiver getting a clear signal so the automatic shutoff will kick in every 5 minutes. WHICH IS A PAIN!!!
If you are planning on using these in a room with lots of electronic stuff then I recommend getting the X1's and just hide the cable.
Other than that this headset is a great buy.