I hope they can give you some answers!
Hi and welcome to the Chiari forum.
I agree with reelman to have a NL take a look at all possibilities,,,,,Chiari comes with other comorbid conditions and many of us have herniated or bulging disks,,,,,so do have someone take a close look ,especially since the muscle relaxers are not helping.
Please keep us posted on how you are doing and what you find out.
There are a couple possibilities in my limited experience. I too have this problem from time to time. Did they do a laminectomy of one or more vertebrae when they did your surgery? Did you have an MRI of your cervical spine prior to surgery? In my case, I had bone spurs in my neck prior to surgery. After surgery, I was diagnosed with bulging discs, and eventually one of them herniated. I also have increased arthritis, which is common after surgery on any joint. You may want to speak with your NL about these possibilities, as the bone spurs can produce a popping sound when the neck moves, and arthritis may be treatable with anti-inflammatory meds. Wish you the best!