Noisy mp3 playback/decoding

I’ve noticed my WDTV Mini is quite noisy when decoding mp3 audio. Other formats such as FLAC or AAC are fine, however mp3 has squealing and modulated background noise. I’ve compared the same material with FLAC and 320 kbps mp3 and the problem is noticeable with the mp3 on the analogue and digital outs.

Seems to be a decoder issue. Anyone else noticed this?

I’ve never noticed this before. Did all the files come from the same source?