How do I get rid of buzzing sound while watching Youtube?

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http://askubuntu.com – So, I'm running Ubuntu 12.04.1 on my iMac G5 and I think I have Gnash installed as a Flash player. The videos on Youtube load fine even though Mozilla tells me from time to time that I need a Flash plugin, I get video image just fine but as for the sound it's all just a scratching buzzing static. Sound works well like testing and listening to music. Please help! (HowTos)