I think it's all of the plates (the black things) that make up part of the transformer that vibrate if they are not tight. The bolt that you say just spins....is there a nut missing from it? Check the other three corners and see whats different about that one
doco Reviewed by doco on . Ballast Noise! I just got the 400 watt hps from htgsupply.com (High Tech Garden Supply) I knew the ballast would make a little noise, and it did for the first few hours it was plugged in, which was fine but then at about five hours the humming started to get way to loud. Is this normal? If so, how do you deal with ballast noise? It gets too hot to just muffle it with a blanket on top. Any ideas? Rating: 5