There is a small signal in low-degree oscillation
data at the beat frequency and its harmonics for
the beat between 15.000 seconds, the MDI basic sample time,
and the SOHO "Major Frame Pulse" which is 14.98828125 seconds,
the ratio 1279*3/256 seconds.  The beat is at 52.12406 microhz
although the observed peaks are multiples of 52.1247 microHz.
Peaks in spectra are seen in whole disk data, i.e. l-0,1,2,3 for the
even modes, i.e. l+m is even.  Peaks up to at least 144
harmonics are seen in spectra of long data series.

Since odd modes, where there is a subtraction of about equal areas on
the disk, do not show the beat peaks, the sasumption is that the
signal is the result of a full disk signal, such as an exposure time
error or offpoint error.

Since MDI and other instruments do housekeeping tasks in response to the
major frame pulse, it could be a beat between an exposure 
and a power drop, or other pertubation.  The source has
not been found.  The amplitude corresponds to a tiny variation
of leas than 1 part in 10,000 of one image exposure about each
5h19m45s.

The peaks in the spectra are very sharp.