I work at a University, and a Professor has a 15 inch 2015 Macbook Pro, and sometimes when he shows a PowerPoint or YouTube video on a projector, through an HDMI cable, the audio sounds slowed down, almost like it is at half speed. We're at a loss. We've tried multiple other laptops in the different classrooms, and can't reproduce the problem. When the Professor plugged his laptop in via HDMI to his TV, apparently it worked fine (I didn't see this, but I trust him). None of my Google searches are turning anything up. We've reset his SMC and NVRAM, but to no avail. Any ideas?