Why do GEVO's make this whining sound?

[Brickrail782]

It can be heard here https://www.youtube.com/watch?v=iKjNd7FvSu0 as the engine throttles up. It can also be heard here https://www.youtube.com/watch?v=mLg_BrqZW3o, but the sound stops and starts again around the middle of the video.

[GenericZack]

Big A** Fans.

[BNSFdude]

It's the sound of the air to air intercooler blowers. They turn on and off depending on charge air temperature.

[NStrains]

That first video looked like they were performing a load test. You can see the exhaust start blowing really good. The second video seems to be more the radiator or intercooler fans kicking on and off.

[Brickrail782]

It's the sound of the air to air intercooler blowers. They turn on and off depending on charge air temperature.

That's kinda of what I thought. Thanks!