[morzh]

Actually the sch shows a speaker WITH hum bucking coil.

Good time to check if it is present in the real speaker.

As for the RC I am not sure it is a resonant trap (or do you mean a snubber?) and whether this kins of things would be effective. It might be simply letting some of the ripple in counter-phase (one goes through inductance, one through a cap) so when they combine at the output transformer's pin they cancel each other.

For a snubber to work here.....something has to resonate.