I have that problem but I also have thyroid disease (Hashimotos)
I'm thinking along the same lines, it could be from MS, a medication side affect or even some other condition eg GERD.
My voice has been periodically going weird for years, (croacky, grainy and disapearing, sometimes i sound like a man lol) for me this has been just another of the odd things that would happen that my dr (of the time) couldn't work out, none of the usual causes ever turned out to be correct. I was a public speaker when it started, and had been a talk-a-holic all my life, so when nothing turned up it was put down to talking too much, seriously like my periodic blurred visual issues (which is now double 24/7) was really from reading too much too. rolf
I did eventually see an ear nose and throat specialist because i'd stopped working, so the dr changed her thinking and thought it was from polop's (sp) or scar tissue from having my tonsils out some years earlier but that wasn't the case either. I'd just had my youngest a few months prior to this again turning up, I also had a few other weird and unexplained things happening at the same time, which wasnt thought to be related to each other back then either. (lol you live and learn)
I didn't have any other types of vocal issues turning up, until I had my big bang in 09, then I developed a stutter and slurred speech along with a few other new ones. That too is periodic and does get better but as time has moved on, like everything else, my vocal issues are more easily prone to happening, when i get over heated and or fatigued, though my vocal issues will also nose dive after my jaw has been playing up too. Honestly though, i couldn't say if my voice has gone weird if i'm doing the slurr/stutter because its pretty hard to get anything out of my mouth whilst thats happening.
We have talked about changing voice issues on the forum, so you might find something interesting in the discussions we're had previously and I know the MS societies (eg msif, msconnections, msworld ) mention it all their sites too, so it wouldn't hurt to go through what they are saying.
Cheers.........JJ
Of course there are other causes as well so it's always good to get your PCP or neurologist to evaluate the problem.
I've had several variations of this myself. Sometimes it seems to be from the severe dryness that several autoimmune diseases cause. Sometimes I think it's a medication side effect. And GERD used to make it worse but I had a surgical repair that eliminated most of that problem.
I do notice on a regular basis that my voice gets raspy and starts to fade in and out and I'm more likely to experience a pressure over my throat area whenever my other MS symptoms are in high gear. It makes sense for me since many of my most troublesome MS symptoms reflect damage in my brain stem.