Audio distortion with Windows 7 Pro on a Dell XPS 8700 SE

What follows is the text of the initial message that I posted at the Dell Desktop Forum regarding this problem:

Running Windows 7 Professional 64 bit, Service Pack 1 on a Dell XPS 8700 Special Edition PC.  I am experiencing audio distortion/breakup & dropouts/skips when playing music from the computer through headphones or external speakers.  The problem occurs whether the source is iTunes, Windows Media or the optical drives.  The longer the listening time, the more frequent & severe the errors become.  When listening to ripped copies of the same music through an iPod connected directly to the audio system or headphones, no errors occur.  I have installed an ASUS Xonar U7 external sound card.  This seems to have improved the overall sound but it has not solved the distortion issue.  The relevant drivers appear to be up to date.  Any suggestions?  Thanks.

After a series of exchanges with Chris M, and performing actions suggested by him that included establishing that the Onboard Audio Controller was disabled & removal of the program REALTEK HIGH DEFINITION AUDIO DRIVER, Chris M's latest reply was:

I do not think that this is a computer hardware issue. The fact that both the Realtek and the 3rd party Xonar both have the issue points to the operating system resource allocation has the problem. You need to repost the issue on the Microsoft Operating System board to get their thoughts and opinions.

So, here I am.  Anyone have any suggestions?

Bill S

Continuing issue:  Following Chris M's reply, I decided to do a clean reinstall of Windows 7 from a DVD supplied by Dell.  I inserted the DVD & rebooted.  After the second appearance of the Dell logo, a screen that I had not seen before (Boot Manager, I think) appeared very briefly.  There were 2 selections & since I did not respond quickly enough, the program defaulted to the first selection, "Windows Setup", which then went to a error screen.  I was prompted to perform certain actions most of which I had already done & then run CMD: CHKDSK /F.

 I do not recall the sequence of events that followed, only that I was getting nowhere.  So, I called Microsoft.  It turned out that I was not speaking with a Microsoft technician, not directly anyway, but with a technician from an offshore company that may or may not have an affiliation with Microsoft.

After 2 days of remote assistance sessions, the "manager" (my case had been upgraded) ran CHKDSK & I think (it was a little vague) he said that he would call me the next day.  CHKDSK ran for about 6 hours & uncovered nothing that I could tell.  The manager did not call me.  I again attempted to reinstall Windows 7 without success.  The day after that I called the company.  The outcome of that call was that there was nothing more that they could do; that it was not a software issue, but rather the hard drive was faulty & that this happened when I attempted the reinstallation.  The issues that was having with the computer that I did not have before were being caused by the faulty hard drive.  I should have a local technician check the hard drive.

So, what do I do?  Should I replace the hard drive?  Is there a possibility that it is the source of the audio problem?  Should I replace the external sound card with an internal one, since the external sound card did not solve the problem?  Should I upgrade to Windows 10?  Might that solve all my problems?

I am sorry that this post is so long.  I will try not to do it again.  I hope somebody has suggestions.  I will be looking.  Thanks for your time.

Bill S