Preview - audio quality

Hi all,

I have a question concerning the audio quality of the previews: Sometimes, especially in my later submissions, the sound is pretty dull, whereas in some of my other clips it is much clearer.

I always choose PCM, 16 bit, 48 KHz and have figured out that when I use Quicktime Pro for encoding the resulting audio is "little endian", because I leave this box chequed, while when I use MPEG Streamclip - uncompressed - it´s "big endian". Nevertheless, that doesn´t seem to be the problem.

Any ideas or suggestions?

Thanks in advance!
Stefan

PS: The sound of the original files is o.k. of course. The question is just about the preview.