What causes distortion?

Hi,

a while ago I bought a Micromega Duo BS da-converter.
After listening to it for a while I noticed there is some distortion in the right channel.

It is not audible while playing music but when the music fades out I hear a kind of distorted echo.

There is also some high frequent noise coming from the unit at high volume levels. Only audible with no music playing......

What could be the cause of this? Maybe a defective capacitor?
The unit is about 5 yrs. old.

Thanks for your opinion.

Matthias.