Mine wasn't speed that started it off carrie but I did find that it didn't happen when I first started the car up, I checked on the mfa and it always seemed to come on after about five minutes of driving and an oil temp of 52 and then squealed away all the time even when I was sat in traffic.

I thought mine was fanbelt but I took my fan belt off so that I could go and get another and reversed the car back a few feet (with no fan belt on) and the car still squealed.
If yours only squeals over 30mph then I doubt it's the belt tensioner
