Jeff has an online radio network that he runs on a series of Mac Minis. But he found a bug in the audio that's causing a whine. Leo says that it's likely from the digital-analog converter (DAC) chip that has failed. He recommends getting a USB DAC, rather than just paying to repair it. The quality audio will be better. But if he has Apple Care Plus, Apple will just replace the logic board.
Jeff says the issue has happened in two of the three Minis he has. Leo says that will likely lead to a recall. But it may also be an electrical issue. Something may be impacting the Mini's electrically. Power conditioning may be the issue.
Leo recommends an app called Bit Perfect ... it's an audio driver that can replace the audio. It's only $10, but it bypasses the Apple software and goes directly to the DAC. If it works, then it's a software issue, not a hardware issue.