So I did install the kit to block the EGR valve holes, and that has obviously fixed the problem. Much much quieter now, and I do believe I have a tad more power. Feels like a smoother shift as well but that's probably just in my head since now it's all been muffled. Or maybe there was a vaccuum leak caused by the egr not being connected properly.

Believe it or not... When I had my muffler replaced, the guy who installed it literally broke off my EGR valve, at the flex pipe. It was laying in the engine compartment wedged underneath some other parts. Which is why I couldn't understand what this hole was for... There was literally a part missing. Moron.