I never got the vibe that either Fred (or Rich back in the day) liked Grande. He seems pretty liked outside of T&R, so I wonder if Gorman let something slip behind the scenes? Or maybe he tried to fuck Wallach somehow?
I believe Fred's hate of Grande is Grande's overinflated opinion of himself. He seems like a guy who can barely get his head through a door due to it being too big. From all the MMA stuff, to the interviews on how he thought they should combine the TV and radio broadcast (featuring himself) to the small stuff the other night about "everyone said the Celtics would be rusty and they overcame!"
Grande doesn't have the TV job and he didn't get it, he's the radio guy that gets put on WZLX if there's a Bruins game on. He's a know it all but still is a regional radio Celtics guy for the most part. I'm not into MMA so maybe I'm missing something, but Grande lacks everything Mike Gorman has which I believe is what puts Fred off.
Also Cedric Maxwell seems to love Wallach which his fuel to the fire on Grande.