Just a heads up. Started my 2010 gen 3 Prius 3 the other day and got a bunch of what I thought was engine clatter and the check engine light came on. Called the Toyota dealer, they said bring it in when I get a chance. The next time I started it, no noise. Anyways brought it to them and they diagnosed it and ordered a new manifold. The next day when the part arrived, I brought in the car. Talked to the mechanic, a great guy, and he explained what happened. Apparently, the clatter is actually the springs rattling in the clutch mechanism of the starter motor/electric motor and not the valves like I thought. Anyways, the mechanic stated that Toyota figured out that sometimes oil accumulates in the manifold somehow causing the noise. Sorry I forgot exactly how the oil creates the noise. But in any case, they ordered a new manifold and installed it in 1.5 hours. The mechanic said this is the first 2010 he has had to do this too but apparently, it's not unusual in past priuses. Apparently, Toyota has been tweaking the manifold to get rid of this because the manifold is actually on the side and below the engine allowing the oil to seep in there. I hope this helps, it was news to me but glad for the relative easy fix and Toyota stepping up quickly, even with a loaner. Oh by the way, it was a technical service bulletin per the service writer so it's on their radar.