nine year old behavior

my nine year old has been talking in a deep throat voice with sudden loud outbursts for two weeks now.  I have tried, punishing, ignoring, taking priveleges away.  I ask him to stop, he acknowledges doing it, says he is sorry and with in seconds is doing this annoying voice again.  Please can you advise me on what to do.  It is driving m whole family crazy.  As we speak, I can hear him talking in his room, with this annoying stupid voice, to himself.  I am really worried.

[RockRose]

Rose,  loosen up,  girl!   For crying out loud.

He's trying to pretend his voice changed.

My sons all did this - all THREE of them - before their voices actually did change.  When their voices changed for real,  it was awhile before I realized the change had taken place,  they'd been talking in deep voice for so long.

Right now,  I've still kept the answering machine message my youngest son recorded in his "deep fake voice" - it's a good memory.  

It's hard to be male.  He's trying to compete with other boys whose voices HAVE changed.