To little level. Remember guitars are not line level, which is around .7v to 1.4v, depending on the source. The instrument level socket on some interfaces is matched to guitars better. If you have a mixer, the line level just has to have the gain turned up too much and this 8s where the hiss comes from, and the burble sound is the low level data probably from a usb connection.
a DI box will let you plug the guitar into the mixer mic inputs which should match better.