[Mondial]

The ground off the bridge rectifier may be a problem, as there is a lot of ripple current flowing at that point. Try experimenting with grounding at various locations, but try to stay away from grounds going between filter caps and rectifier. A connection right at the negative terminals of the big filters may be ok. The negative terminal of the bridge should go directly to the filter cap negatives not to chassis so that all the pulsating rectified dc goes directly to the filters without any other paths through the chassis.