Hi Tobo and bduffy,
I’m experiencing this problem too. With Mac OSx 10.6 I don’t had this problem.
I did a clean installation of Mountain Lion, and I started having problems with dropouts and crackles - both with Cubase 6 (6.5.0 - 6.5.4) and iTunes/Websites 
I use Macbook Pro and MR816x (Version 1.7.4 of “TOOLS for MR” ) + Cubase 6.5.4.
Has anyone found a solution?