The pinging could be the OPD valve, but it would be strange that both are doing it. It could be rapid movement of the regulator that is being transmitted and amplified by the mounting. Disconnect the regulator from the bracket and see if it stops.
Hope this helps
Jim & Debbie England
Do you have Gas? 2015 F350 6.2L CCLB DRW 4.30 axle. 2012 Yellowstone Ridgeline 34RLT Fifth Wheel