Exhaust vent noise

Alright,
I got some loud noised from all the exhaust in my room (from the light exhaust to A/C exhaust). Outside it gets pretty loud if you come within 10 feet of them.... Anyone have any way to cover up the noise or stop it?

Is it from vibrations?

It sounds just like exhaust air to me... like a loud fan is blowing my grow room's building away Its not like vibration of the vents itself. If any vibration its from the air being bounced off the walls of my output boxes before it exits...

Put an inline muffler in. simple to make. If your running 6" exhaust, just buy a 10" or 12" dia. round duct pipe from homedepot, with 6"to 10"or 6" to 12" reducers on each end. The longer the better. before you snap the duct together, glue in some !/2 inch insulation on the inside walls of the duct pipe. put it in before the vent exits to the outside. $20.00 and it might work..........