Cars been experiencing a metallic buzzy rattle at 2700rpm for a few days and I suspected it was the cat heat shield. I've just popped it into the exhaust place for them to check it out and there were four bolts missing ftom the cat heat shield. They've replaced them now and the buzz has disappeared, I'm surprised that four had come loose and fallen out.

Thought I'd post this as others were experiencing a similar noise so it's probably the same that's happened to theirs. Simple fix and they didn't even charge me.

 

Yep very common, they tend to rust and break off rather than coming loose