Whining noise - Pointy.

I had this exact problem a few weeks back, even happened in exactly the same speed range, and I naively thought I'd just ignore it until it got worse. It ended up just disappearing.
It definitely sounded like it was coming from the front end of the bike though, not sure if that's the case for you.

Let me know if greasing the speedometer sensor fixes it, was first on my list of things to try out if it got worse.

[buckstone]

I had exactly the same thing. Thought it was a wheel bearing at first, but checked them and they were fine. Really bugged me for a couple of weeks then it stopped as quickly as it started.

Probably not a lot of help, but at least you know you're not alone !!!