Root canal/permanent crown work completed 6 wks ago. crown hurts with dull pain when tapped. return to dentists for xray and gums check. no issues per dentist except teeth grinding. no other teeth hurt. any suggestions please? no issues prior to this?

Pain is a warning sign, it is likely there's inflamation at the end of the tooth which has been root canal treated. Was the tooth comfortable after the root canal and before the crown was made? If it was it may be incorrect occlusion. Recheck

Have your Dentist check your occlusion to make sure that the crown is not microscopically "high." If there are no occlusal interferences would recommend that you see a root canal specialist, an Endodontist, who is best trained and has the best equipment to evaluate for root fracture, residual untreated canal, periapical infection, etc.