Well the working version:
from direct.showbase.ShowBase import ShowBase
from pandac.PandaModules import *
import struct
class MyApp(ShowBase):
def __init__(self):
ShowBase.__init__(self)
source = UserDataAudio(11025,2)
data = str()
for x in range(11025*5*2):
data += struct.pack('h',0) #only changed line
source.append(data)
source.done()
sound = base.sfxManagerList[0].getSound(source)
sound.play()
app = MyApp()
app.run()
So you see only one single line has changed. The clou was to provide the rawdata as signed short and not as unsigned short so I had to fix my importer-module.