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Check that you do not connect common ground of your PIC and motor. If so
you need to separate them. If they separated then the problem is in
relay's inductance.Check if you have proper decoupling capacitors near
to PIC (it was discussed in the List)
Tha problem may occure if  power rises above 7 V due to any reason. And
this can not be disabled. Check your power supply engineering - DOES IT
HAVE ENOUGH POWER TO SUPPRESS EMF?
The better idea is opto coupler with triac to control a motor that fully
decoupled motor circuit from control circuit.

Regards,
Vassili