I know exactly what sound your talking about with the blowers. It's like a humming sound. This is what I did. I took a steel C-Clamp and tightened it onto the motor of blower. The C-Clamp absorbs the vibration from the blower and humming sound goes away.
hey everyone, have searched the forum and web for sound suppression ideas without success. what do you guys use to reduce the sound from the venting fans. i'm running a 170 cfm and a 440 cfm fan
got the fan problem solved by using a variable speed controller to dial the things down to the amount of air i need. still have louder than desired air flow but i'm adding a duct muffler and insulated ducting.