2014 death rattle

I have a 2014 Prius with the death rattle. I have no loss of coolant and I have cleaned out the intake manifold and also the Erg valve. It rattles only when it’s from a cold start. If I accelerate before it runs a cycle it won’t do the death rattle. Every once in a while it will hesitate when turning a corner. Had a mechanic look it over and he said he didn’t see anything wrong with the coolant and I should replace the upstream O2 sensor. After cleaning out the IM the check engine light has not been back on. I have also put some fuel injector cleaning through it. Any thoughts on what to do next?

 

219000 on it. I clean out the little holes on the manifold with brake cleaner and small wire brush. I clean it out about 2 weeks ago now.

when you first turn on the Prius and you hear it start up and it runs for about 15 seconds is what I refer to it running a cycle.

The code was p301 I believe

 

Once I turn the car on and it’s been about 5 to 10 seconds I hear the engine turn on and that’s when I get the death rattle.(the high pitch sound it makes before it actually runs) The rattle has lasted anywhere from 10 to 20 seconds. If I go ahead and give it gas before the engine starts running it doesn’t rattle but I can feel/hear the misfire.