You'll have to watch and see.
When my chicks were several weeks old and living on the screened porch I got too close to the porch with the lawnmower and caused a pile up.
Two chicks were crushed badly at the bottom of the pile up, but fortunately they survived.
Some chicks it might not bother at all.
You guys! its just a vacuum and theyre just chickens!
They learn by repetition. No matter what the outcome is with your vacuum adventure today, be sure to do it every single day, even if they do pile up, freak out, or generally have little aviary panic attacks- eventually they'll get over it.
Especially if theyre young- which they must be since theyre in the brooder still.
My cockerel doesnt get too upset by the noise but the sight of it really sets him off. I cant get him to calm down until I get the thing out of his sight. He flew off the porch the first time he saw it, in an effort to get away from the "monster."