2011 MBA Problems

[vtyler98]

I have a 2011 MBA which randomly freezes at times, whether I'm on the internet or in pages, or sometimes there won't even be any application open and I'll come see my computer frozen. I don't use Chrome and it had this problem under Lion, took it to the Apple store twice and they ran some 48 hour tests on it but were unable to duplicate the problem so they did a clean install, but I'm still having problems with it now. I upgrade to Mountain Lion but the freezing issues still exist, I'm not sure what else to do since Apple says it isn't a hardware problem, and I've not been able to figure out if there is any application causing it as it never happens with the same applications open, it is always different and sometimes it has happened right after rebooting my computer with nothing open yet. No error message pops up and I've tried the standard reset of PRAM and SMC which didn't work either. Any ideas or suggestions?