Video failure when changing to HDMI sound & Skype crippled

[Coming_Curse]

I use Linux Mint Nadia 64 bit on a Toshiba Laptop (Satellite L650D) with a Radeon 5650. Whenever I switch to HDMI output first everything seems normal. But when I enable sound output via HDMI in the sound settings every video I watch is speeded up and no sound appears no matter if its a DVD or a flash video.
Additionally - I don't know if this is related - when I run Skype the first 1 or 2 seconds of each new sound are crippled. If I speak to someone longer it is no problem, only the first seconds appear this way.
Can you help me please to get this solved?