so I am now a physic car problem diagnoser

Hey man my buddy has a car issue “i’ve been hearing a rattling noise from the engine, almost reminds me of popcorn popping. it only seems to happen when i’m at speed on the highway... what i’ve managed to find online where people had similar problems it all seems to say it only happens when the engine is still cold or UNTIL people get to speed.”
Any idea? Not heat shield or exhaust

have some shots of my local McLaren dealer