Audio crackling & increasing lag w/ USB interface

When recording with my guitar-to-USB interface, it is impossible to record with any more than 5 or 6 tracks. When I do, I get a loud crackling noise as I'm recording and with each round of crackles the lag increases so much that it becomes unusable. The only way to get around this problem is to mute all but a few tracks when I am recording, but this causes problems when I'm trying to match up different instruments' rhythms, etc. The audio buffer in Audio MIDI Setup Utility is set to 44,100 like it should be, and I have no other programs open and nothing else plugged into the computer. I have a MacBook Pro w/ Retina Display that's less than a year old, with an SSD and 8GB of RAM so I am very surprised and disappointed that the hardware can't seem to handle recording a basic song. Is there any way to solve this? Thank you all.