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Answer found... incase you all wonder why.
the actual reason for the problem is not known, at least by anyone outside Apple, running Garage Band resets certain audio settings in the operating system that restore audio functionality for other applications. This has a lot to do with that 44.1k versus 48k audio rates setting that we mentioned before. Sometimes, an application will set your Mac to use the 48k audio format, and this can cause problems with other applications. Launching Garage Band will reset your Mac to the 44.1k format. Of course, you can also check your audio setting in Applications / Utilities / Audio MIDI Setup. In the Audio Devices section, check that your Audio Output format is set to 44100.0 Hz.
 
Yeah I had the same problem with my old iMac, launching Garageband then quitting would solve it. It was really frustrating till I found the solution!
 
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