Hi.. Thanks for the query. Stiffness of the jaws along with popping and pain with ringing in ears is appearing to be due to disturbances in the functioning of the jaw joint.. Due to clicking and grinding sounds you can experienced ringing in ear too.. However muffled hearing is not due to it so once you should also get an Otoscopy of your ear done.. You should get a Panoromic x ray done so that the jaw joints can be examined and the exact cause can be ruled out and treated.. As of now take anti inflammatory painkillers like Ibuprofen and muscle relaxant like Tizanidine.. Take soft diet and avoid excess mouth opening like during yawning and laughing.. Hope this helps.. Regards..