I don't think anyone has really tried what you're asking. Most people will use the fans all the time. You should just try what you think. If it works then great and if it doesn't then you know next time. If the fans or smell become a problem just cover the hole and take out fans. The worst you can do is kill the crop but it sounds like if your parents find it then that would be worst. And if you kill your crop then you will know next time that it doesn't work. I know killing a crop really sucks and is a major setback but it may give you a chance to learn something new. If you decide to do the fan just do like the other people said and hook it up to run slower. Are you in the planning/building stage of your op? Also, I know I read some stuff on here recently about these people who are building grow boxes out of dressers. You may want to look for those threads. Another good idea would be to get a mini fridge and grow in that. Get one with a lock. Then there has to be noise coming out of that thing. And you can claim to your parents your just lazy and don't want to go to the fridge. I think you can find a crappy one on craigslist or something if you don't have much money. I read some people doing that too.