I have a dxz575usb HU that makes a low clicking noise when using the usb only. anyone else have this problem? can be heard at low volume levels like 1 or during silent parts of music. if you have a similar HU (575/675/775) and dont have this problem, are your speakers hooked up directly to the HU or to an amp? Ive tried mp3/aac/wma, 128-320 CBR/VBR, 44.1k/48k SR, FAT/FAT32. and learned that a higher bitrate makes the clicking sound faster...