Nasty rattle under car

[Krhuangbin]

I posted this in the dedicated brand forum section on here, but I also thought i'd cast my net wider by asking in the home mechanics section

My car has developed a nasty harsh rattle from the underside somewhere, which specialist completely missed during service and misdiagnosed it as exhaust valves (they are fine/locked open.) I can't pinpoint it on my own, seems to echo down whole exhaust

It's not engine.

Link to video here:
https://www.youtube.com/shorts/S-WWW6uMZ7s

-It's not present at all when cold
-Seems (as can be heard) to resonate at 2k-ish revs
-Is a lot worse when the car is warm, then left for 10 mins or so, then started again., before settling again.
-It from somewhere under car - NOT engine - engine is perfectly sweet, just serviced, new belt, valve clearances done last year etc. Noise nowhere near engine
-In the video, you can hear the rattling slightly at idle at the start, then a LOT when revving
-Happens the same at standstill or moving, at same revs.

Car is a V8 Vantage. The Cats came off and were re-installed about 3k miles ago/1 year.

I'm thinking either a loose heat shield somewhere, or clamp bolt? Or does that sound like a broken up cat? Or a leak even? The only when warm may be a clue?

Any ideas as to what that sound may be, very gratefully received

[Nexus Icon]

If it's spectacularly tinny it's almost certainly a heatshield. A broken cat sounded like a biscuit tin full of pebbles on a friend's MX5.

[RSTurboPaul]

+1 for a heatshield being loose.

[zedx19]

Loose heat shield or baffles in a silencer blown, both rattle like mad.

[Krhuangbin]

Thanks all, will get under and tap around for a source

[kambites]

Another possibility is an exhaust hanger (or the bushing of one). As the exhaust warms up it will expand which could bring it close enough to touch something as it vibrates. That will typically give a slightly lower-pitched rattle than something like a heat shield.