I'm having the exact same issues!
Our Samsumg HL-S5088W experiences intermittent sound distortion. The best way to describe it is that it sounds tinny with all voices sounding like they have a lisp. We originally thought that it was the HD feed from Comcast, but just discovered tonight that it has to be the TV. We had cable on and it was making the noise, so my husband decided to play his XBox--moving the HDMI cable from the cable box to the XBox. It is still making the sound. We also tried external speakers, and it still made the sound. We've found that it lasts no more than 24 hours and happens maybe once or twice a month.
I've seen postings about other sound issues with Samsung, but did not see anything about this anomaly.
Have you ever heard about this issue before, and if so, any suggestions?