As soon as you see the first signs of an aura, taste a little salt. If it tastes good, take a gram or so.
Best if you have capsules, but impossible to get here...I make them for SWMBO, who suffers from migraine. She has to take a lot, and it controls the condition. No doctor will tell you this, but there is a lot of research out there to back it up.
I have to make 200 - 300 capsules a month, 300mg each.
I, like you, get occasional migraine aura, no headache. Salt works for me, but I only get them occasionally, less than one a month.
I would not be at all surprised if your tinnitus were a manifestation of migraine without headache.
Do let me know if it works or not!