Rattle on ICE kick-in (low RPM)

My 2010 prius has started making a metallic rattle while driving, It only occurs when ICE starts or stops and goes away other times.Typically low RPM. You can hear it in the cabin. I can almost have it come on constantly when the Hybrid system indicator is past the middle bar and I keep it there.

I crawled under today and checked the heat shields starting from the front to back. But all seemed to be firm with no screws loose or missing - nothing seemed out of place - the shield under the cat converter is held on by plastic rivet like things but that was also not that lose. While under in front I reached in to check the heat shield in the engine compartment where the exhaust joins the engine. That was also firm.

I have about 150k on the odometer and changed the spark plugs and the inverter and engine coolant last year.

I'm really out of ideas on what could be doing this. Any thoughts?

 

I don’t have a theft proof shield for the cat. Also the EGR circuit has not been cleaned, although this doesn’t sound like the problem. @xliderider we had loosened that bolt while changing the bulb recently, but I tightened and rechecked, and it is not that.

I attach a file I recorded on my phone and the noise kicks in at 6 seconds or so - sorry not the best quality

 

Well, I did an experiment while I was under- I tied that shield with 2 separate zip ties extending in different directions. So it stopped moving. Still got the rattle, so I ruled it out.

 

For serious??!