Suavie,
Mine only does it if the Disable Mute Confirmation Tone is set to No. When it is set to Yes then I don't hear it on the Mitel 5000 phone. In either case I don't hear it on the far side of the conversation.
System > Flags > Disable Mute Confirmation Tone: Yes
Which side is hearing this and what version of software is the system running?
Thanks,
TE