Motorola has had a grounding issue with their equipment from the past and has implemented a "grounding strap" that is sent with their 870-MHz BLE's and MB's. They have a number of these "band-aids" stuck via an adhesive (that falls off when you touch it) on both the top of the modules and the bottom as so it yields a better ground to the housing chassis when the lid is closed. Unfortunately, most of these "straps" fall off and are never reattached and the system tech has to deal with the issues. This strap is obviously much cheaper for Mortorola than fixing the grounding issue with a "permanent strap" that would cost them a few cents more.
Without actually seeing the problem you explain, I can only assume that you have checked to see that all the module and module cover screws exist and are tight as are all housings connectors that might disrupt the ground. Another assumption is that you have confirmed that no corrosion exists anywhere in the connections and that you have also checked that the "fins" on the actual module (RF) are not flat or missing as so it can make a proper RF ground.
If this does not help, please be more specific on the type of units you have, your output levels, channel loading and where in the cascade this is happening.
Good luck!
