MOTM

>Feeling a bit dorky at the moment,

The first time I saw the *output* from a sound card being used as a square
wave generator on a 'scope I thought "where are all the harmonics?--is
something acting like a resonating filter?" I switched to DC and it looked
the same, and then it hit me--low sampling rate.

This is the image that popped into my mind when I first read your post, but
as it happens it sounds like that's not what was happening in this case,
and Paul and Scott are probably dead on.
-- 

Terry Bowman, KA4HJH
"The Mac Doctor"

"It gets calls when nothing else works"--Walter Eugene Scott, PdD,
explaining somewhat facetiously why a "TV preacher" was smoking a cigar.