Grow Room Crackling sound

[Darthweeder]

Hi!

So.. I got an exhaust/fan that is making these crackling sounds.
I've almost always had them, it seems tho as they came after I started to use a speed modifier (not sure what it's called in English). Don't think they were there when the fan was going on full strength.
Could it be something to worry about?

 

[AutoWonders]

What does it sound like without speed controller?