Noises

[Brownstoo]

I'll take off on my trusty phazer and get up to about 40k and then this strange whistling noise (Can't really describe it better than a 'fluttering whistle') starts, so I slow down and start to drop below about 40k and it disappears. It happens no matter what gear/revs I use.
It also never does that if I just sit there at 6k revs in neutral. It also sounds like it's coming from under the tank or near the front somewhere, but I can't really tell 'cause it only happens when I'm on the bike and moving.
Wtf is going on?

[dieseldave]

I have this on my ute. My aerial is a piece of Aluminiun welding rod with a hook (for safety) on the end. If the hook is facing into the wind at the correct angle it starts singing/whistling at about 100k. Quite useful as a backup speed monitoring device.

[Brownstoo]

Aha! Using my powers of deduction and a whole lot of trial and error I've found it's my speedo/speedo cable.
Any particular reason a speedo would make a horribly loud noise?
I greased the cable and the drive and put a bit of grease in the back of the instrument panel where the cable goes but that didn't help.