This has happened three times now. On first starting the car in the morning it makes a nasty mechanical noise for a second. The first time it happened, the car had sat two days without being used (the weekend). Then Monday morning it made the noise when started, lasted no more than two seconds. The next two times (not in a row) it had sat just overnight and the noise only lasted a second or less. The car is parked in my driveway, which is sloped, with the nose up. I measured the slope using the door jamb and it measures 17°. I don't think the noise is starter solenoid not disengaging (I've heard that on other cars and it sounds different).

Is this oil starvation? Oil level is normal (measured on level surface of course). I've never had any car do this before on the same driveway. And it's only done it 3 times out of x,xxx times I've parked like that.

 

This is fairly common. Google "tsx noise on start up". Causes and results vary slightly. Most commonly, I believe, it seems to be a VTC actuator.

 

I've had my actuator replaced twice, now the TSB says that the sound will not cause damage, and that it's the valve that makes the noise. My car is currently at Acura having the timing chain replaced because it's apparently stretched. I have 101,000 miles, I don't think it's just a coincidence. But that's just my .02. Is this the sound:

 

I don't really hear the sound on your video. I'm Parking the car with the nose down in the driveway now... just in case. Haven't heard the sound since. But it's very sporadic - may not happen again for a while.

 

Strange. Well...has the car ever been run low on oil? A stretched chain makes sense. But why is it stretched? A worn TCT will cause a rattle as well.