[PROBLEM]
We've tried ~5 different MP2 encoders (including tooLame, AWave, etc...)
and did some listening tests.
The results were incredibly bad! We took a piece of Jazz music, some Pop songs and one from Dave Matthews Band...
There was a really audible high frequency noise (9.5kHz and 11kHz) on all files, but it was hardly noticable within the Pop-songs (of course...)
[SOLUTION]
We just couldn't believe that THIS was the default for broadcasters and you will never believe what we found out:
It weren't the encoders, but we've used Sequoia and Windows Media Player for playback and they seem to use the same decoder.
Playing it back with a different decoder revealed a smooth sound!
(e.g. NOA BWF Player)