Hi GoonieG,
The screen brightness should not be causing any change in the fan functionality or there be any sound. Since you are experiencing this sound issue, I recommend you to flash BIOS from the link given in the previous post and also make sure the air vents are clean and the system is placed on a hard surface where there is good air circulation.
If the issue persists send me a private message with the system service tag to check the system details. Click on my name and click Start Conversation to send me a private message.