What gain are you set on ? It could be that you are right on the verge of clipping and songs that are recorded a bit "hot" break over into clipping.
One concept that seems to need repeating at regular intervals is that the O2 is a bit different in how it gets to a clipping level. Unlike about every
other amp out there, the volume control on the O2 does not influence clipping levels, but the gain setting for input level does.
Good observation, but he said he's using a Bifrost as a source, and even at the highest gain, there should not be clipping at the amount he's describing. It's not like he has it plugged into his computer's 3.5mm out and is playing at 10% OS volume.