Sparky, With all all programs except Go Back, disabled by 'Unticking' in MSCONFIG and rebooting, problem still exists. Remove Go Back and problem disappears.

Alec, my hard drive was defragmented just last week, but just to take one 'variable' out of the equation, I ran the defrag program again this morning, then disabled all background programs, except Go Back, using MSCONFIG and rebooted.
I then tried the recording process again using 'Audio Recorder' via USB - same result - distorted recording after about one minute. Without doing anything else, I then recorded the same sequence using the Windows Recorder - Result? Perfect recording
So, I guess I'll use that method. QED