I've got a late 2013 27" iMac running the latest OS X (Mavericks 10.9.1). When recording audio through a USB device (I've tried both a USB headset and a USB Mixer (Alesis iO2 + condenser mic) I sometimes get a very crackling recording. I've tried the same hardware on my 2011 Macbook Pro, running Snow Leopard, and it seems to work fine. A Google search is leading me to believe this is related to late 2013 Macs (specifically, those running fusion drives) and USB recording devices, but I can't quite see why this would be.
Has anyone experienced this issue before? The problem also seems to be quite random - I have had clear recordings as well as crackled ones, without changing any settings or unplugging anything. The only other thing I can think of is that the length of recording might be having an impact, but so far my tests have all been well under 1 minute.
Any suggestions welcome.