Dvina that Vietnamese had at that time did not have any technical fixes to counter modulated noise jamming (or other types of jamming) effectively.
For SAM operators, the only instruction was to turn off ARU/VARU and tune RRU knob so that the jamming strobe is as narrow as possible. But this couldn't have helped much against B-52. As Vietnamese had not much help on the hardware fixes from Russians, their only hope was to compensate in tactics - echelon the SAM batteries in such a way that at least one battery will get a good angle where jamming is not so strong. This is how most of B-52's were shot down - they got a firing solution when B-52 bomb bay doors were open (increases RCS) or during a post-target turn.
I can only speculate, but it would be very resonable to guess, that in Volkhov (> mod3, 1972 and later), GShV mode should eliminate or weaken the modulation effect (shooting rules recommend GShV mode on in jamming conditions), as long as jamming does not overload the compensation channel.
Volkhov mod3 and also later mods of Dvina (SA-75MK) had a fix called IARU (Impulse Automatic Gain Control) to counter strong noise jamming (like from B-52). It reduces the receiver gain according to ARU voltage level (which depends to the jamming intensity) on-receive during the time period that corresponds to the range above the horizontal distance marker. Supposedly, this extends the dynamic range by 25dB and rises saturation threshold. IARU effectively narrows the jamming strobe above the horizontal range mark on beta/epsilon indicators, so operators can track in angles more precisely in manual mode, as illustrated below. Range information is fed from RD-75 Amazonka (if available) or from I-87V/TT instrument. IARU mode is not compatible with GShV.