Some of our buses fans are noisier than all get out. Can't hear the radio (dispatch). Others are super quiet and give off really nice air.
I did a little research and it appears that, yes, the shape of the fan does make a difference. I would also imagine how the blade flexes, not at all or a lot, can make a difference in the noise and harmonics.
I found this brand mentioned for RVs, which should be much quieter than trucks or buses, so the noise level of the fans might be lower???
I tried searching using the word "decibels" but not surprisingly, nothing came up. The manufactures probably don't want to discuss that topic much.
Best of luck.