| I assume the dimmers are solid state. What is the brand and model? How many lights on each dimmer? Many electricians put in inexpensive 60 w. A-19 lamps (regular light bulbs) unless something better was specified and they buzz a lot. Good quality lamps (ie, Sylvania from an electrical supply house not Home Depot) will probably solve most of the problem. Perhaps your fixture will take a halogen PAR lamp. If you don't know, give us the model and brand. This is Lutron's advice:
Overview
A solid-state dimmer is an electronic switch that
rapidly turns the current on and off 120 times per
second to produce the dimming effect. This rapid
switching can cause incandescent lamp filaments to
vibrate, resulting in a buzzing noise. Lamp buzz is
generally noisiest at mid-range (50%) dimming level.
Some lamps are noisier than others when dimmed,
depending on the physical characteristics of the lamp
filament. Lamps of higher wattage (100W and
above) tend to produce a louder buzz. Therefore,
use a lower wattage lamp whenever possible to
reduce lamp buzz. Other factors that affect perceived noise level of lamp
buzz are:
• Pitch of lamp buzz
• Type of light fixture
• Ambient noise level of room
• Surrounding surfaces/finishes
• Relative proximity of light fixture to ears
• Individual sensitivity to noise Recommendations
• Use lower wattage lamps (100W or less)
whenever possible
• Selecting another brand of lamp can sometimes
reduce lamp buzz
• Use a physically smaller lamp
• Upgrade to a specification grade dimmer Lamp Debuzzing Coils (LDCs)
The most effective way to reduce lamp buzz is to
install a lamp debuzzing coil (LDC) into the lighting
circuit. When an LDC is wired in series with the
dimmer, it slows down the in-rush of current during
the rapid switching cycle of the dimmer. As the
current inrush is slowed down, the lamp filament
vibration and lamp buzz are reduced.
Lutron has two LDC models available to help reduce
lamp buzz. The type of LDC required depends on
the total wattage of the dimmer’s lighting load. Listed
below are the model numbers and their respective
capacities. Note: For loads under 600W, call the
toll-free Lutron Hotline: 1-800-523-9466.
Model Rated Capacity
LDC-10-TCP 600-1200W
LDC-16-TCP 1201-1920W
LDCs may be wired in series with the dimmer on its
line side or load side. Each dimmer requires its own
LDC.
Lutron is a registered trademark of Lutron Electronics Co., Inc.
During normal operation, LDCs may make an audible
buzz and, therefore, should be mounted in an area
where the noise will not be objectionable (e.g., an
electrical closet, a basement, or above a drop
ceiling). | 
