Cyko_01: does it make your voice go higher or lower when inhaled?
Menkhaf: I guess it was a joke, but it should be rather simple to determine: if the gas if lighter than the atmosphere you're breathing, your voice will be lighter if you inhale this.
sploxx: To be more specific, the molecular weight of normal He to He with one muon attached is roughly 4.1/4.0. The change in pitch relative to breathing He should be the square root of that ratio, which is a change of about 1.2%. For someone with absolute pitch, it may be possible to hear the difference of tone of a musical instrument. But I doubt anyone will hear a difference when a person speaks.