Hey Di-
Sorry about the neck annoyances...no fun! The cracking and creaking is caused from the wearing down on the pads between the discs (kinda like when the brakes go on your car)
I don't have MS, but my husband does. Of course, he doesn't listen to me regarding his neck issues

I got over some pretty serious disc disease with exercise and supplements.
Most MSers have cervical spine issues, whether or not they have lesions on the spine. My hubby has a lesion at C2, and wearing in the disc padding at C5.
Do you have a cervical spine lesion?
I really recommend yoga...getting into certain positions like "downward facing dog" will stretch your spine and neck, and help alleviate some of the constriction. Maybe find a local class, easy or beginners' level. That's how I started at the age of forty!
http://www.yogajournal.com/poses/491
Most of us jam our necks when we talk on the phone or work on the computer, and the discs start to "grind" together. (Like Jimmylegs lovely static description) Plus stress and dealing with MS can start to wear on your neck.
Supplements like MSM, glucosamine and omega 3 oils will help replenish the padding that grows in between the discs, and exercise will create space in between the discs, so the padding can fill in and stop the cracking.
If you haven't had an xray or MRI of your cervical spine, you might want to ask for one, just to make sure everthing's OK.
Welcome to the baords, and I hope you find some relief!
best,
the aging cheerleader
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Husband dx RRMS 3/07
dx dual jugular vein stenosis (CCSVI) 4/09
dual stents placed 5/09
CCSVI in MS