I, too, experience this quite often. Unfortunately, 90% of my occurances are of the hallucinatory type. It used to happen to be about 5 times a week, but it has since slowed down to about 2-3 times a month. With me, I experience the same things many of you mentioned, such as the loud buzzine sound (it's so fuggin' loud, that it feels as though my eardrums will burst). Also, I always have my eyes open rather than closed so it makes it worse.
Anyway, I have seen some of the scraiest shit in my life while experience SP. I can't tell you how many times I have seen spirits and/or demonish like figures. I have even had them attack me on rare instances. I would fo into it further, but I'm not sure how many people would blieve it to be true, some of it's so bad.
I have done a small amount of research on this, and the basics of it are that somehow it opens you up to things you would not normally be open to receive (obviously). They don't know the exact cause of it, but there are supposedly meds that can help. I believe I saw somewhere that there's a prticular drug that completely eliminates it in like 40% of patients (although I cn't remember the name of it). Also, one researcher gave these stats...
80% of people who got SP got it only while laying on their back
30% on their sides
30% on their stomach
Obviously, that's not 100%. It's simply a percentage based upon position of sleep, meaning that some people fell into more than one category. Anyway, hit me up on AIM if you want to talk.
And I would also like to welcome myself to the forums here
Chris
AIM: MORPHeusBreakz