Hi, Kimbob,
I understand what you're going through right now. I have pulsatile tinnitus in my right ear, too. It is constant, and I've had a number of tests, but no cause has been found so far.
I'm glad you're going for an MRI in 2 weeks. Have you asked about having an MRA and/or MRV at the same time? Those tests are for arteries (MRA) and veins (MRV), and can be performed at the same time as your MRI. That way, you could be sure that there was no problem in either your arteries or veins that might be a potential cause. I had an MRA, and they injected a dye into my veins for that test. They didn't find anything, but at least I was able to rule out any problems with my arteries.
Aside from that, the best thing you can do right now is to remain calm, so you don't aggravate your condition, and try to distract your mind as best you can. I've found that works well for me.
Good luck, and I hope you'll update us after you've had the MRI.
Best wishes,
Karen