A low pass fitler designed for ~30MHz ought to help.
Look up a low pass fitler desinged for ham transmitters.
Cehck oyour local public library for the ARRL Ham Handbook.
They have featured good designs before.
You may have to add some RFI control on the power cord as well.
Corecom makes some nice RFI IEC(PC power cord) style fitlers.
If the case isn't metal you might want to find some copper screen and
line the inside of the case to stop direct pickup.

Strong, close RF sources can be beat, but it requires some work

And don't feel too bad about an on topic post, it will be one of
very few today.

Terry