Odd buzzing sound when cold out

[Apex3]

It's only happened 2 or 3 times, but it still worries me. A couple of times when it was <20 out this loud constant buzzing noise would start coming out from under the dash when I'd go over ~40mph, then would shut off under ~30mph no lights coming on or anything, just the buzzing, loud enough that I could hear it through my stereo turned up as loud as I can stand. It's clearly something electronic, not a mechanical piece, and it is not coming out of my speakers.

Any ideas what could be causing this? Is it something I should worry about?

[Apex3]

Scratch that, got some help elsewhere, nearly certain it's a bad relay, making the same noise my ABS relay was.

[magicmike]

Sure its not the speedo cable??

[07Evolved]

mine was the speedo cable...

[ericem]

Your wipers on by any chance?

[Apex3]

Could be speedo cable too, I haven't tried to fix it yet. I'll try to narrow down where it's coming from next time I hear it Thanks.

[Apex3]

So it's definitely the speedo cable, the buzzing changes with the speed, and my speedometer started going all crazy today. Is this something I need to replace? Or is something just loose that needs to be soldered or something?

[BSOD2600]

My speedo does this too when its below ~25 F. I bet its because the lube around the flexible cable shaft has gotten hard from the cold. either hope the friction will heat it up.... or I bet prolonged use in this state will eventually make the cable break prematurely due to the increased friction/wear.