Anyone can give a message you have posted a score of 1 to 5, 1 being poor, 5 being excellent. The Noise drop-down allows you to specify the minimum score a message must have in order for it to appear normally on the boards.
Voting is weighted based on membership level. A new (non-status or bronze member) has a voting weight of 1. Silver members have a weight of 2, gold a weight of 4 and platinum members have a weight of 8. Thus a vote of 4 and a vote of 5 will not necessarily result in a score of 4.5 for a message.
If a message has been given a score that is below your noise threshold then it will appear dimmed out on the boards. A message must have at least 3 votes and be below your threshold to be grayed out.
Messages that have been voted greater than 4.5 will be marked as red regardless of the the number of votes it has.