SDL_mixer playing ogg files produces noisy background

Hi all !

So I am playing an ogg file via Mix_FadeInMusicPos but unlike as with mp3 files I can hear a strange knocking allthrough the music.
To stop that Ive increased the prebuffer size in Mix_OpenAudio( to 40968 bytes) , still no change. But choosing a higher buffer size(i.e. 409616 bytes)
always resulted in an error message : “Fragment size must be a power of two”.
Could there be another reason for ogg files doing such a noise ? (P4M-1500Mhz max. 5%cpu usage, unstable/testing Debian GNU/Linux, SDL 1.2 from the testing package)
Is 4096*16 not a power of two ? Am I requesting too much ?
Am I in the wrong mailing list ? (This is my favourite one :))

Regards ,
Marc Essinger <@Marc_Essinger>