GarageBand random cracking/spike when playing

Good day,

I've only just started playing my guitar through GarageBand. I own an 8 gb RAM Macbook Air, and connect the guitar to the notebook through a Line 6 Pod.

When I play to hear myself, adding amp effects, I randomly hear a short, high pitch sound, with cracking. At first, I thought it might be because of my guitar, for it kind of sounds as if the output port on the guitar has an issue...that sound produced by high gain amplifiers when you tap the tip of the cable. BUT I then changed to a clean setting, and I got the same distorted sound, which would be improbable on a clean channel.

Is it custom for it to happen on notebooks such as the Macbook Air? I mean, it's no Pro, mind you, but it does have 8 gb of ram. I don't record with it, just play for fun to hear myself on the speakers.

No lag when playing back, whatsoever, I might add.

Is it a fault from Garageband?