You might see a chiropractor. They can be amazing in filling in the mechanical effects of activity.
A limitation of the MRI is that it is static, also though, we are supine in a position that most of us don't even sleep in. I get a (maybe not so) similar pain from rib distraction at T 1 and T2 . It radiates in the same pattern to T 4-5.
You might also see a PT. A really good one will tell you exactly which muscles. Best luck.