Pain in RCT treated tooth is not possible as the nerves are not there within the root canals..there must be some high points on the crown so your biting forces are not equally distributed ...its causing stress to Periodontal ligament.. so pain occurs due to pressure point
Next Steps
Go to concerned dentist .. get an IOPAR XRAY done of that tooth..to check whether there is any periapcal or periodontal radiolucency..
Health Tips
Visit dentist as soon as possible.. warm rinse will not help.. crown height needs to b corrected