Baffle noise should be hiss-like. Lower frequency motor noises could be from bearings or fan imbalance. Fan blade tip turbulence depends on the tip speed, and the ModernAire may be using a slower speed/larger blade diameter than the Prestige. Duct noise can be all over the place, as not only does it have turbulence noise, but it can amplify (in the sense of an organ pipe) particular frequencies driven from the other noise sources.

A rubber hose "stethoscope" may help locate the source of the noises. Removing baffles for testing can also help.

When possible two 45deg bends is perferable to one 90 deg bend. Sharp turns will affect the noise level of the vent. The harder it is to push the air the more noisy it will be.

If you think it is just from the filters try running it with 1 or all the filters removed to see if there is a major sound difference. There will be some difference but it probably won't be major.

I will try it without the baffles but I fear that it could be the two 90 degree turns. The Modernaire duct goes straight out the wall it's on. It sounds like air movement, not mechanical however, I'm not sure. I will investigate further this weekend when I'm down there. Thanks!!!

@cheri127 what did you end up finding here? Am curious if the baffles on the Prestige hood end up making a difference vs. ModernAire!

The function of the baffles (besides being a firestop) is to extract grease particles from the larger end of the grease particle spectrum by centrifugal impingement as the air stream has to make two 180-degree turns getting to the inside of the hood. This process requires enough air velocity, but also good baffle design, forcing reversals at constrained pressure loss. Noise depends on the turbulence inherent in this process that in turn depends on how aerodynamic the baffle shapes are. No one is going to make NACA shape baffles. They will all be stamped and roughly trough shaped. I think baffle hiss will be inherent in all functional designs. It is possible that higher end hood fabricators have selected shapes that are a bit less noisy.

Where blowers are used in hoods instead of remotely, the noise from blade tip turbulence will be immediately above the cook. This noise should be inherently louder than baffle noise due to the CFM being generated on smaller surface areas. Further, the blower design and rotation rate is restricted by volume available for CFM being claimed, whereas remote blowers can use axial and centrifugal designs that can utilize lower tip speeds and perhaps more CFM per dB designs.

I have never examined a Modernaire or Prestige hood so I can't speculate on what specific differences might lead to the observed noise performance.