I got my 46a650 Late january (2009), and I have the same problem. Normally, the tv turns off fine, but when there is no signal on hdmi, and I turn off the tv, it seems to happen. As long as I turn off the tv within reasonable amount of time, after i turn off my ps3 for example, it is fine. Another workaround is if you change the signal source (for example from HDMI1 to TV) before turning it off, it seems fine.
It is annoying, yes, but I decided keep it. My first 46a650 had different kind problem with hdmi, and I really don't wanna go through another replacement process.
I recently bought a Samsung LN46A650 LCD TV. I've had it just for a few days, and the other day, when i turned it off, a horrible screeching, crackling sound came out from the TV. I don't even use the TV speakers (i have a home audio system) but just knowing that this is happening for such a new TV is a big problem i think, and i hope it doesn't cause anything else to go wrong. This seems to only happen when i have the TV on for more than an hour or so. The other weird part is i go into the TV settings and turn the TV speakers to "OFF" and it STILL happens. So, then, i'm thinking it's the cables, HDMI or Optical Audio, so i unplug everything and turn the tv on and off and the sound is there again.
This sound does not happen ALL the time, but it does happen and it's a huge annoyance. I called Samsung and they said they have never heard of this problem before, EVER. So, anyways, im just curios if anyone here has heard of this and if you have, what's the problem and how can i get it fixed??
Thanks.

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