[Latitude 28]

Funny you should have this problem....we had the same issue a week ago while at an RV park.  Only reason I suspected 120 volts is a night light I had plugged in by the drivers seat would go out when the buzzing started.  I checked the AC volt meter in the overhead L1 was 121 volts and L2 showed 100 volts.  By the time I got to the pedestal my surge protector showed that L2 had gone to 5 volts.  Had the breaker changed and all is well ever since. Having said all that to get to my point.  When he relay is buzzing check you AC volt meter to see if there is an anomaly going on.