I have a PCM2704 sound card connected to my Raspberry PI. It works well, without audio glitches and the sound quality is good but there is one problem. It is not detected on power up. removing and replacing the USB connector causes it to be detected and operate normally. the command 'lsusb' shows the device absent until disconnected and reconnected. After a 'shutdown -r now' the USB sound card comes up working. Does anyone have an idea how I might fix this?