Engine rattle after head gasket replaced

Replaced the head gasket 15K miles ago. Did everything by the book, cleaned the EGR valve and cooler, intake manifold ports, used quality parts, new head bolts, followed all torque specs etc. New plugs, reused coil packs. Current mileage 287,284. Doesn’t burn oil! Suddenly after running like a champ I’m getting what sounds like the death rattle at cold startup. Coolant level has not changed. No codes unless I’m not letting it run long enough to trigger a misfire code. I shut it down when the rattle happens. Thoughts?

 

Thanks for all he replies. When I did the job I put new plugs in, cleaned the EGR valve and cooler, cleaned the fool out of everything then cleaned some more to include the ports in the intake, had the head checked and decked. Reused the injectors with new seals. Fuel mileage has never gotten back to the average 49 and hovers around 40. Yesterday I topped the coolant off to be exactly on the full mark, could have been more than a couple of tablespoons. Now, chances are the EGR was never replaced. I bought it at around 232K miles and it had been well maintained. I found a YouTube about checking the EGR valve by removing the top bolt from the pipe at the EGR valve and sliding a putty knife in there and retightening the bottom bolt. I was able to drive it yesterday to get it to operating temp and then I put the putty knife in. This morning it started normally. Over the next few days I’ll idle it to temp and shut it off, watch the coolant level, and try a cold start each morning. I’ll also take an oil sample and run it through our lab at work (CAT dealer) to see if there is any traces of coolant. Here’s the video I referenced. It it turns out to be the EGR valve I’d be overjoyed at spending $160 bucks and replacing it vs. having to go deep again.

 

I haven’t been able to work on the Prius for a couple of weeks. I removed the bottom guard and found the inspection plate for the damper and popped it off. There are no pieces of springs laying in the bottom. I started the vehicle multiple times, climbing under the car each time to watch and listen during the actual startup. It will rattle/knock with each start but then clears up. It may seem louder with that inspection plate off but that might be psychological. I can’t see anything else in there. Is there a better way to inspect the damper. How would I know for sure? Nothing else is making sense at this point. Coolant is still dead on the full mark and I tested the egr valve by blocking it off. Still did it.