TV's Frink said:

Bale's voice is so annoying, it single-handedly destroyed the movie for me. I don't care if it makes sense or not, it's not something I want to listen to.

This. I think it's a number of things. One Bale trying to disguise his accent while bringing up the gravel. Two, I want to put some blame on the cowl. It looks like they modified a scuba mask and it seems to have the same effect on the voice as one would. Very nasally and ugly. Combine the two and you have one of the worst voices ever.

Thankfully Dark Knight was the Joker's film and so Batman is not featured prominently at all. That I think saved it. No way Bale Batman could have carried it. I think we're in for a real perfect storm of terrible voices with this new Bane. Nolan must be partially deaf.

Edit: I also can't express enough how much I hate his cowl. The designers didn't take into account at all how it looked on the actor. They can't have...