I have read that NMDA agonists (DXM, Ketamine, PCP, other arylcyclohexamines) work pretty well for this. Anecdotally, their withdrawal symptoms include tinnitus so I'm not surprised the inverse could be true.

It also looks like more specific NMDA agonists are being developed as a treatment? http://journals.plos.org/plosone/article?id=10.1371/journal....