Okay, I'm on my 2nd BB Tour from Sprint and I had this problem with the first one too. My tones (ringtones, message tones AND alarm tones) change randomly on their own. They might be my settings one call and the next call I get could be totally random. It's very random and annoying, and I used my warranty to get a new phone because I thought it was the device, but the new one I got does the exact same thing. It happened like a month after the frist one, and it's not even been a month since I got this one. I just got my very first one in September.
I just noticed this last night with mine. (Verizon tour running .61) Did a little digging, and it turned out it was any contact I had edited recently. Somehow it created a "custom" profile for those people that consisted of random tones, none of which I had selected. If I went to sounds/custom profiles there were a bunch of people in that list that shouldn't have been there, and the only commonality was that I had edited their info recently (be it pin, cell number, etc). Just deleted them from the list and it seemed to be back to normal. Weird thing is, it didn't happen with new contacts I've added, only old ones I've modified. Not sure if this will help all of your problems... but it's worth checking out!
Went into Sounds then Set Contact Alerts and found that list. Yep. All were recently edited contacts. Deleted them all so we'll see if that was the issue.