If you’re using the rFactor lite install, I have (for a long time) noticed a horrid noise on some circuits, in different locations. Turns out the the Crowd ambience file is wrong. Apparently this affect all rFactorLite installs.
So here is the correct working file: Download
Extract it to your [rfactor Install Folder]\GameData\Sounds\Ambient and overwrite the incorrect file.
You’ll need 7zip: Get it here