Hectic buzz sound when using Mac VST plug-ins

Every time I try to export something from an Ableton Live project that uses Mac VSTs such as AuPeakLimiter; I get an insane buzzing sound through my speakers/monitors/headphones. The exports are also the same buzz, which I obviously can't use for my work.

I bought a brand new MBP a week ago to replace my old machine, but now for some reason using my old DAW, plugins, setup etc don't work anymore.

I love the Mac VSTs and it's actually one of the main reasons why I bought another MBP.

Has anyone else had this issue? I need help please, because to get out my old machine every time I want to do an export is going to drue me nuts.

Any help would be greatly appreciated.

Thanks very much!