iMac high pitch sound (4th iMac in a week). Any improvements?

Hello,

I know there is a lot of forum posts on the internet about this, as I've spent about two days reading them (primarily from my iPhone as my screen sound drives me up the wall).

As some people have experienced, this is a result of changing the brightness (0% and 100% are fine, anything in between emits a high pitched whine...some people believe this is a result of the capacitors vibrating at around 15-16Hz, which would make sense).

I have actually gone through four separate iMacs in a week to try to fix this problem (and two being upgrades over the model I had in hopes of a different production run). I have checked the serial number on all of them and they were all build between September and October, at various weeks between, mostly within a 4 week window.

I am beyond my wits with this issue and not sure what to do now. I have spent nearly 20 hours setting up four separate computers only to format them to take back in a chance I am lucky enough to get one that I can dim at night time without getting a ringing sound in my ear.

I was wondering if anyone else who has experienced this issue has come across a solution, or at least a replacement that has worked? I am debating to go for number five, but honestly, I am almost too tired of boxing and driving, boxing and drive (rinse and repeat). (I even tried three separate stores in hopes to get a different production week that didn't have this issue).

Looking forward to your responses, and any guidance. I love this machine and I wish it just stopped having these issues so I could do some work...

Setup(s):

First two:

21.5" iMac 3.06GHz Intel Core i3
4GB RAM
500GB HDD
ATI Radeon 4670

Next two:

21.5" iMac 3.2GHz Intel Core i3
4GB RAM
1TB HDD
ATI Radeon 5670

Thank you,
Adam