I have two windows side by side in my room. Last night, I tried to open one in order to get some fresh air in. It's always been a little hard to open but I managed to open it a crack. All of a sudden, I start hearing this fairly loud rattling/vibration coming from the other window (The one I hadn't touched). It wasn't constant, but kept coming and going throughout the night. I closed the open window to see if it would help but it still continued. Weird thing is, if I press on the window while it's shaking/vibrating, it stops. But obviously, I can't do that all the time. What's going on here? I've never had this issue before. Anybody know how to fix it? It's driving me crazy!