short of virus/malware, i'd check the most obvious:
keyclone -> setup -> override settings ->
[X] overlay reminder
message [mute]
color [anything but black!]

next to that, i assume your situation is: you on PC1 with keycloneA and WoW running, gf on PC2 with keycloneB and WoW running.

if so, check if both keyclones are connected to each other so if you press the "mute" button on PC1, it will reflect that on PC2. uhm just in case - to connect keyclones: type in the "computer name" or the "internal IP address" and the "port number" separated by a colon, on the connect textbox at the bottom of keyclone's main interface (ie Connect [192.168.0.5:1320])

other than that, i'd check if what your pressing corresponds to the actual 'mute' hotkey in keyclone -> setup -> override settings -> override hotkey