Could my permanent retainer be the cause of my tmj / tinnitus?

Very unlikely: See a dentist who has extensive training and experience in tmd examine you and determine the cause of your symptoms. Also pose this question to the orthodontist who gave you your retainer.

Probably other cause: It is more probable that the orthodontic treatments would be more related to your problems than the retainer. Orthodontics should be done to the best functional bite position, but orthodontic treatments are usually done to whatever bite position happens to occur and this relationship may be dysfunctional.

Unlikely: It is unlikely that a permanent retainer would be the cause of a tmj/tinnitis issue.

Hard to say.: Possible. See the doc who placed the retainer. If no satisfaction, see a TMJ specialist. Any dentist can be a TMJ expert with the proper training and experience. Most commonly, oral surgeons, prosthodontists, and orofacial pain specialists. Ask your MD, your dentist and your dental society for referrals.