Have you tried other games? If you have the disc version of GT6 it might well be the disc but if it persists in other games you should try re-entering safe mode and selecting "rebuild database". Beware, it will delete messages and I'm pretty sure music track information (artist, album etc) so you should back them up on USB drive.
Try that and post your results!
I tried GT5 and did watched a 20 B-spec race, there were no problems
I've had that a couple of times but I'm not 100% sure how I fixed it. Those slim PS3's are a bugger for hoarding dust in the vents and just under the top cover (got the same console bought at the same time) so try that first. What you're seeing might be a sign of thermal throttling. If that fails and as a last resort, do the game updates again.
You may be on to something. The fan is very loud when ever I play.
I took a brush to the vents on the front and back, but there was no lint or debris. But I noticed the bottom seemed pretty hot. I got an empty wine bag from a three liter box of wine and filled it with cool water. I set the PS3 on top of it.
So the next night, while the PS3 was sitting on it's little water bed, I ran my room and fan never went above medium speed. I had no visual problems like in the video above. Tomorrow I am going to stop on my way home from work and get a can of compressed air and crack the PS3 open and blow it out. I have had 2 cats for most of the life of the thing, so I am pretty sure that the heat exchanger is probably pretty hairy.
But, the night before last I had a weird new problem. The PS3 was not over heating the fan was on low or medium all night.
At the end of a race, there was no results screen and the cars seemed to autodrive around for longer than normal. Then the other cars dissapeared, and I was left autodriving around the track all by myself. I had to quit the game and it reset the console with a triple beep. I was hosting and the whole room got kicked.
Last night the first two races, the same thing happened. I restarted the room and left, to let a friend host. This time the same thing happened but it did not destroy the room just me.
Today I deleted the 20 GB game data, and went through the 21 updates. It took about 2 hours and 45 minutes. I get about 85 Mbps download speed.
I will update after I run my room tonight.