265 Engine rattle noise under load

Hi all, in a Meg 3 RS 265 with a flash tune, I'm trying to diagnose an engine rattle noise when accelerating between 4-6k rpm. Took it to a mechanic and he couldn't find anything in suspension or exhaust or anything. It doesn't feel like it's misfiring or lacking power. One mechanic said a possible manifold leak, another mechanic said it wasn't. I'm at a bit of a loss... has anyone else had a similar noise?

Audio clip here, you can hear a rattlie/ticking at higher rpm under load:
https://drive.google.com/file/d/1J2-IRxP9qIRfOSw3Gd8wfE59bASHS27Q/view?usp=drive_link