gearbox

I'm trying to identify the source of this buzzing sound. Setup: -Gen2 gearbox rebuilt and fitted with a Quaife lsd. Fitted on my gen 1. -Rey's cables. -CS stage 2 rmm. Hardrace (OEM+, full rubber) side mounts. It shifts perfectly, works well, no problem. Oil is fresh - Motorsport CRX LS 75w90...