Backlight make buzzing sound

jyavenard, it is possible that this is caused by one of the transformers on the inverter board. Those are located at the general vicinity of what you described. They are definitely replaceable, but we would need to know exactly what board your display has, as well as who makes your LCD panel. Apple of course does not sell the inverter separate to anyone. With a bit of luck and some investigating, I am certain that the part can be found. BTW, what about warranty. May be you could try that route as well. Take this answer as coming from someone who is not a Mac person :-) Oh yes, do not forget what Apple recommends in the service manual for noise, hum vibration:"

Noise / Hum / Vibration

• Buzzing noise

• Rattling noise

• Ticking noise

• Squeaking noise

Quick Check

1. Verify display’s USB and Mini DisplayPort connectors are plugged into known-good supported system with up-to-date system software.

2. Tilt display to hinge limits to determine if mechanical noise is generated by the hinge mechanism. Repair/replace mechanism if needed.

3. Play sound sample at loud and soft volume levels to determine if noise is caused by the left/right/ subwoofer speakers or the amplifier circuit.

See Audio Issues.

4. Verify that air intake/outflow vents are not obstructed, inducing a high fan speed.

Deep Dive

Check Result Action Code

1. Disconnect AC power cord, remove glass and LCD panel, disconnect left, right, and subwoofer speaker cables from logic board. Then reconnect MagSafe, DisplayPort and USB cables to a powered-on computer. Verify if noise has disappeared.

Result Yes Audio issue with speakers or amplifier. Go to Audio Issues.

Result No Go to step 2.

2. Verify that ambient air temp sensor is correctly positioned on fan and securely connected to logic board, and that LCD temp sensor is securely connected to its connector on back of LCD panel, and properly protected by insulating foam.

Result Yes Go to step 4

Result No Reseat sensors connectors / readjust sensor position/

foam protection and retest

3. Determine if noise issue sounds like fan is running unusually fast.

Result Yes Replace ambient temp sensor cable.

Result No Go to step 4.

4. Remove fan and inspect blades for damage or obstructions.

Result Yes Replace fan.

Result No Go to step 5.

5. Remove fan and rotate blades. Verify that fan blades spin smoothly without interference from fan housing.

Result Yes Go to step 6.

Result No Replace fan. Retest.

6. Reinstall fan while carefully ensuring that there are no cables routed under or near fan assembly that might cause interference with the fan blades. After reassembling verify that noise is resolved.

Result Yes Noise issue resolved.

Result No Replace fan. Reconnect all cables, reinstall LCD panel and retest.

Hope this helps, good luck

for mine, I determined from other threads that the bundle cable coming out the back of the display was bad. in addition to the hissing noise, my display would go blank intermittently. a bit of work to open the display and replace the cable, but it worked... display is on consistently, no noise. HTH.

My 27" display was making a very annoying buzzing sound. I took off the glass and unscrewed the 8 bolts on either side and took off the top. There was a lot of dust. I used a canned air cleaner to blow away all of the dust, then replaced the entire assembly and so far no more buzzing sound! I hope it will stay like this.