Laning against Rumble is so freaking annoying.
His Q has such an annoying medium range for the harass, along on a short cooldown, it's just annoying as hell.
He can disengage if you decided to all in him, or he can just kill you as he outdamages you with or without his ult.
His poking is beyond annoying, can't go up to cs without him just turning towards you with Q, take some damage, then turns around and repeats this over and over again as it's on a 5 second cd if I remember.
Worse of all is that he's worse to lane against than some other lane bullies(Renekton, Darius, Garen) as he can go all in on u, and still have tools to get out without worry.
I don't think he is overpowered by any means, he's just a TAD overtuned as his laning is freaking annoying to play against, I hate laning against Rumble ALMOST as much as Riven.
And that's saying something.

Here's your counter.