I have two vinyl, single hung windows, side by side in my bedroom. My house was built in 2004. Ever since the house was built, I'm hearing a "SNAP" sound coming from one of the windows. When the house was first built, I figured I was hearing settling sounds. Both windows work fine, stay up fine. There's no timed, rhythm to the sound, just at any given moment, I hear "SNAP" from one of them. This has been going on for 8 years. I'm mechanically inclined, but have never ventured into window repair. Any advice on what's going on and how to repair would be greatly appreciated.