Loose connection in the radio's antenna.
If the pump isn't running, no electricity is flowing; therefore no RFI.
The vibration from the priming into loaded-with-water could have broken an already weak connection.
I'll complain bitterly about that POS 'Entertainment System' too! But you've got antenna wiring issues to be fixed.
TT 2015 19RD "TheJayco"
TV 2003 F-350 "Montblanc" - Housebroken chore truck
Sitting in The Cheap Seats.
And proud of it!