Set was purchased in spring 2005, original lamp still in use. No problems when powering on from a cold start.
If the set has been in use within the last 30 minutes or so, there is a fairly loud whirling noise which increases in pitch before ramping back down and repeating. The lamp is lit (can see light through vent slots on back) but there is no video on the screen.
Letting the set rest for a while cures the problem.
UPDATE I cleaned the inside of the set out, blasting away a fair amount of dust. The lamp looks fine, no obvious indications it has burnt out. Reassembled things and plugged the power back in.
Now I get one of two behaviors. If the lamp does not fire up, I get the whirling sound described in my first post. The set cannot be set down via the front panel button; rather, the power cord must be physically removed.
If the lamp does light up, I get the source indicator graphic (Composite1, AV1, HDMI, etc) in the upper left corner and the source feed for a few seconds. Then the image freezes, goes to black followed by a quick grey bar flashing horizontally across the middle of the screen, then the set "resets" itself as if the power were just turned on and repeats the entire process. The green lamp light on the front panel button never goes on and I have no functionality with that button. The only way out once again is to pull the power cord.