I corrected a similar problem after discovering that the contact between the sled and the RioCar was less than snug. I had to bend the sled tangs so that there was a more forceful sliding contact when the unit was inserted into the dash.

You might check that the metal "bumps" on your sled are still makng positive contact with the metal shell of your empeg. And that the metal shell in the dash is itself reliably grounded.

Intermittant problems can be a bear to nail down.