That loud humming sound

[WeatherSTARIII]

Has anyone notice, if you listen carefully, you can hear a loud humming sound in the background from the old Forecast Center set. Here's what I'm talking about:
 
Video 1

http://www.youtube.com/watch?v=p-W6LiPPdUw

Video 2
http://www.youtube.com/watch?v=ZOHccqGsVY4 (The video's owner prevents external embedding)
 
You can even hear it whenever they would get to the maps. Here's an example in the first video with Dave Schwartz:
http://www.youtube.com/watch?v=58EpWyX9BxQ (The video's owner prevents external embedding)
 
So I was woundering, could it be some low buget air vents?

[lfmusiclover]

I believe the humming noise is simply the sounds of the computers and other equipment in the studio. With as much equipment as there is in there, your bound to hear some noise. 

[WeatherSTARIII]

But I notice that the loud humming was gone back when TWC got their new set in 1997. Maybe their old studio wasn't soundproof like it is now. 

[lfmusiclover]

Probably so. And you also have to consider that technology has gotten quieter over the years as well.