Is the ballast noisy itself? (electrical hum) Try putting rubber feet on it? Like from a custom PC build website. They have lots of noise silencing tricks for computer cases.
A fan based air cleaner can make a fair amount of cover noise. I have a dehumidifier and an air cleaner running in the basement where my grow tent is hidden. It's enough background noise that no one will look for anything else.
A fan based air cleaner can make a fair amount of cover noise. I have a dehumidifier and an air cleaner running in the basement where my grow tent is hidden. It's enough background noise that no one will look for anything else.