I experience this intermittently, not typically on system startup, but occasionally when going into/out of game titles or disc or movie download playback back to the XMB.
I believe what we've got here is an issue w/ HDMI/source HD standard switching, as my consistent 'fix' is to cycle my TV through its inputs and back to the HDMI input for the PS3. Works every time. Try this versus a power cycle and see if that works. Pain, yes, but maybe it'll get resolved in future software updates.