If you are using the Heil CC-1-Y mic cable from Heil Sound with your FLEX-5000, you may experience RFI issues due to the way some of these cables are wired.
The FLEX-5000's microphone input is essentially balanced in nature and as such provides has exceptional characteristics for preventing RFI from getting into the radio even in high RF environments. However, if the mic cable is wired in an unbalanced configuration, this will defeat the RFI mitigation advantages of the balanced input.
So how should the microphone cable be wired?
The 8-Pin Foster connector on the FLEX-5000 is pinned out like Yaesu radio. See the legend below"
Pin1 - Not Connected
Pin2 - +5 VDC (65 mA)
Pin3 - Not Connected
Pin4 - Not Connected
Pin5 - Chassis Ground (Shield)
Pin6- PTT +
Pin7 - Mic -
Pin8 - Mic +
With CC-1-Y cables that exhibit RFI issues, the mic cable shield is connected to both Pin5 and Pin7. And the cable shield is not bonded (connected) to the shell of the 8-Pin Foster connector. This wiring configuration defeats the balanced nature of the mic input.
This can be easily tested with a ohm meter. If there is continuity or 0 ohms between Pin5 and Pin7, then the cable is wired for an un-balanced configuration,
To correct this problem, remove the electrical connection or bond between Pin5 and Pin7. Also make sure that the cable shield, which should be connected to Pin5 is also connected to the shell of the 8-pin Foster connector. This should resolve any RFI issue you experiencing related to using the CC-1-Y mic cable with the FLEX-5000.