On higher humidity days I get a very loud hum on the bottom end of the am
band on the radio in my garage caused by the overhead fluorescent lighting.
Is this from the tube or the ballast? On less humid days the hum is still
there but not overpowering.
Hum as opposed to buzz?
Try grounding the fluorescent reflector.
It will probably be a ground problem somewhere in the circuit. Check
for an ungrounded outlet nearby. Hard to suggest a specific thing
without knowing exactly what the circuit looks like.
You seem to have localized it to the light - turning the light off
makes the hum go away . . . Ground the reflector to a known good
ground. The light may be the obvious source of the problem but
something else may be a contributing factor.
My wife had a turntable that would buzz at the power line frequency.
I tried everything I could think of including running a wire to a
stake in the ground.
It turned out to be the missing ground on the power transformer
supplying the house. I was out mowing the lawn one day and noticed
there was no ground on the pole. I worked in power line construction
and knew it is required. It looked like someone stole the copper. I
called the power company and told them about it - they added a ground
at the pole and the turntable buzz problem was fixed.
The ground is required for the lightening arrestors on the transformer
to work - there was no argument from the company they just added a
ground the next day. Pays to look around the pole now and then - a
lightening strike can vaporize the arrestors (a collection of broken
porcelain and carbon disks around the base of the pole). Power
company will fix that too - and if they don't you can lose every
electrical thing in the house and the house . . .