Hello my friend, I'd like to give you a little hope and let you know that you're not alone in having this EXACT issue!
I recently had a problem I came to this forum looking for help too. However people did not take me seriously. I got replies telling me it's this and that! That's it's my computer, BUT guess what rest assured, IT'S NOT!
I felt uneasy being a newcomer to the forum seeing hatred thrown my way after I re-stated it was NOT my hardware over and over again, as if I didn't matter.
In turn I alone figured out the answer to this problem. Turned out it wasn't so complicated as people made it out to be. Thing is I use Windows.
All I need to know is what audio driver you are using for your reason settings, because I know that MAC has it's own proprietary sound drivers. If I can answer after that, I will. But, I can't guarantee I'll be able to based on what your settings are. If you are using the proprietary MAC sound driver, all I can say is that it is NOT your computer and it actually has nothing to do with the hardware of your system but HOW your driver USES your system!
I hope I helped and can further assist you, unlike some people here, even though I've never took on the role of helping someone out on a forum. And if I am not able to point the problem out to you directly at least you'll know it's not your computer and won't be going crazy about the possibility your computer is useless.