Ipod producing distorted sound when playing high frequencies

When I play certain tracks on my iPod Classic (5th gen.) there is noticeable distortion during loud, high-pitched passages. It is like the clipping effect you get when a high frequency signal is cut or compressed.

At first I thought the fault was in the sound files themselves but most of the problematic ones are in ALAC format and should be OK. Sure enough, they sound fine when played through iTunes on my computer or through my SmartRadio.

So the problem is with the iPod. Is it just this model or is my individual iPod faulty and, if so, can it be fixed?