Chris is correct. If you have a slide out kitchen, your refrig has a cooling fan on the back side that kicks on when the temps are high on the coils. Mine is very noisey and runs for quite a while, especially if it's a warm day. When camping and it's hot, I sometimes remove the black plastic vent cover on the outside of the slide out to let out some of the hot air and it seems to help. I have read that there are replacement 12V computer fans that are quite a bit quieter so I'm going to order one and give it a try. Mine is very accessible and easy to replace.