On the 747-400 there is no squelch button or knob, but if you press and hold down the , i.e. VHF 1 button for a second or two, you get the squelch function. Ergo, can now listen a little further away than you normally would.
As for the morons that yap away on guard, I will have no sympathy for them if someday they find themselves in need of assistance and find none.
If you want to yap, use 123.45. Stay off of guard unless you truly need it.
I really wish the Brits would have a dedicated practice frequency. The volume is practically turned off all the way across England. England is by far the worst area in the world for un-necessary noise on guard.