It is not very loud at all. Like Jimbare says, if the doghouse is properly insulated you hardly hear it. I driven my truck with it the lid open, then it is noisy. It is a treat to drive with it open when your trouble shooting. You can see it you have a water leak or how smooth or rough the engine runs while driving. But when closed it is pretty quiet that you can talk to the person in the passenger seat. There is some noise, but nothing that will take your hearing away.