troubleshoot

The source of the noise is USB, since it uses a 24MHz clock and the
spurs are 12MHz apart. The views' amplitude range auto-scales based on
signal strength of transmitters present.  In a typical environment with
wireless access points, mice, keyboards and the like transmitting
between -55 and -35 dBm, the USB noise is barely noticeable.  In an
anechoic chamber with no transmitters present, the way the views
auto-scale does cause the spurs to be shown off to alarming affect.