When I play non-protected WMA files of 64 kbps and 44khz which have been ripped without changing anything from video on my Clip+ I get a garbled sound.
Usually this means the WMA file is mixed into some kind of odd ASF stream that our parser doesn't understand. Regardless, you should go to the bug tracker (link on your left) and post such a file.
The unexpected thing is that they all play normally w/ the Sansa firmware(Sansa firmware's volume is too soft for my taste
).
We don't support the Sandisk software here, but if you change the region to "USA" the original firmware will have the same volume as rockbox. Its only quieter if you set it to an EU country.