Iriver x20 - headphone output gone weird

I bought this unit like 3 days ago... it was great. Loved it... used it 4 or 5 times no worries. Got up this morning to go for a run and found that the sound was really weird. Pulled the headphones out and the speakers on the unit sounded fine. Swapped out headphones... exactly the same problem... like you could hear all the backup singing and stuff but the main vocals were gone... and no bass.. and it sounded all crunchy...