Sounds like you've got a startup entry from the IDT version of that Sigmatel driver, which probably came from Microsoft, not Dell.   IDT bought Sigmatel, but their versions of those original drivers can cause problems.    I have the identical Sigmatel device on my 410,  but it's the original one from Dell, and does not have an sttray entry anywhere.

In any case, give a "clean" driver install a try:

1) Download the original Dell Sigmatel audio driver from below, but don't run it yet.   When you download, don't use the Download Manager, just choose the browser option - one less hassle.

http://support.dell.com/support/downloads/download.aspx?c=us&cs=22&l=en&s=dfh&releaseid=R124105&SystemID=DIM_PNT_9200C_XPS_210&servicetag=&os=WW1&osl=en&deviceid=8907&devlib=0&typecnt=0&vercnt=1&catid=-1&impid=-1&formatcnt=0&libid=3&typeid=-1&dateid=-1&formatid=-1&fileid=165080

2) Now, go to Add/Remove Programs, and remove Sigmatel.

3) Go to device manager - right click My Computer, Manage, Device Manager.   Scroll down to Sounds/Video/Game, right click Sigmatel, click Uninstall.

4) Reboot the computer.  The "Add Hardware" wizard should pop up.   Don't do anything - just cancel it.   Now, go back to the file you downloaded, double click, and install it.

Hopefully this will return it to "original" and you won't see that error again.