The radio is probably not the problem.
The RFI is only present when the HVAC blower is activated ( and varies in pitch with blower speed), right?
Given that, it would seem to me that the blower motor is causing the RFI . This could be caused either by a poor ground connection or internal arcing across the commutators/brushes. The radio is just picking that signal up.
You could install a filter in the hot wire to the radio - just snip & strip the wire and buttsplice it in - or you could check and repair the root problem - i.e. the blower motor.
Grounding:
If you have A/C there is a heavy gauge black wire that runs from the blower housing to a bolted ground connection at the firewall. Release the connection, clean the threads of both the bolt and the internal ones on the firewall - clean the connnector faces as well. Secure the bolt tightly.
You must be registered for see images attach
If you don't have A/C the motor is grounded through the fan casing. Pull the motor and fan assembly from the housing by removing the 5 little bolts around the perimeter. Clean the flange facces of both the blower housing and the motor casing. Clean the threads of the fasteners as described above. Reinstall and make up tight.
You must be registered for see images attach
If that doesn't help, the probem is sparking across the commuator bars and brush faces. It is a simple job to clean the commutator and undercut the micas.
Check the grounding circuit first and see what happens.