Rode NT1 5th Generation New Microphone Fault Straight Out The Box? Muffled Rumble Issue & Repair Update

So I recently got a pair of them and one of them was making a muffled rumbling sound when handling if you tapped on the front of the grille/capsule or body it would sound VERY different to the other paired microphone so there was obviously something different between the two. I got a replacement but had the same issue. Now I have sent it off to Source Distribution/hhb for a repair. I am really hoping it comes back fixed. It should arrive there today as its out for delivery already. Anyone else had dodgy mics on arrival from any brand? I had this a few times with condenser mics. It makes me feel like I am being picky with the mic quality when I just expect something working properly and matching at that price point. They are not £30 mics.