Don't want to distract too far from OP's question, but is one of your panels sub-fed from the other; this is very different than having 2 meters.
If sub-fed, only the main panel should have ground and neutral bonded with each other. The ground bus should be isolated from the neutral bus (green wires separated from white wires) in the sub-fed panel.
The issue/problem if ground and neutral are bonded in 2 places is the ground and neutral conductors between those 2 places are now essentially parallel conductors connecting the same points: so that the neutral current is split with some running through the (green) ground conductor. The problem with this is ohms law. A current running through a conductor (that has resistance) will create a voltage across that resistance (conductor), this is a problem because everything connected to the (green wire) ground conductors should be at 0 volts (grounded). These are things people touch. So now, because current is flowing on the ground conductor, everything people touch (metal enclosures, equipment cases, etc..) connected to the (green wires) ground has a voltage NOT zero. This could be a shock hazard (though most likely just a little trickle). A bigger problem becomes if a neutral or ground connection then fails and the whole ground system (and metal cases connected) goes to 120V.