Ok lads,
Here are Rudd's tips for expert mumble use.
Keybinds -
Go 'settings' -> 'shortcuts'
Make sure you have buttons for
Force centre - This is your 'radio' to talk to everyone in your sub channel.
i.e. if you are in the iGi channel, sub channel SL team 1, only those in the SL sub channel will hear you.
DO NOT USE FORCE CENTER IF YOU AREN'T IN A SPECIALISED CHANNEL. Or you will force me to alt tab and kick you. 
Volume - There are times when you don't need to hear mumble and need to hear something else. This isn't a fault with mumble, even when I'm on St John Ambulance duty I need to turn the radio down to talk to other people, or deal with the casualty. I just turn it down to the level that I can hear if my callsign is being called. I do the same with mumble if I need to do something requiring quiet. e.g. the start of the round, SLs are talking to eachother and I need to assign kits to my squad.
This also helps balance your game volume against mumble volume without having to Alt Tab.
There are 2 buttons you need,
DECREASE VOLUME BY 10%, and INCREASE VOLUME BY 10%.
With these simple keybinds you will find your mumble experiences more positive.
