your first video contain a very accurate depiction of a modulated noise jamming effects on SA-2, from 20:30, with a nice zoom-in at 20:50.
This is how it's explained in SAM operators training manuals ('statut boevovo primeneniya'):
A noise jamming creates a jamming strobe. But a periodic amplitude modulation to this noise (a sine wave) that is just slightly miss-matched (within 1-3Hz) from a scan frequency of Fan-Song (16Hz), creates the effect of jamming strobe (or its centre of brighteness, more precisely) moving around sideways, as if rotating around some invisible vertical axis on the scope.
This makes it difficult for an operator to keep a steady track on the centre of a jamming strobe and reduces the effectiveness of a manual tracking.
According to my sources, this form of jamming (noise jamming modulated at a scan frequency), especially used from several aircraft flying in a pod formation, was considered the most effective form of jamming against SA-2 by russian SAM engineers.
Sadly, there is no english or russian sub to the videos... there are some other interesting information!
Indeed! This video is pretty good, I'm glad I found it!
@Jonas85, did you find a way operators could deal with this modulated jamming...?