x2 I do this every other weekend it seems. My home is in the process of getting a bit of work done by me and I've made quite a few trips to Home Deport for lumber, rolls of deck carpet, and other large bulky items. If I couldn't drive with an open rear window I'd have been driving around last weekend with a trailer containing six 2x4x8's and eight 8' quarter round molding sections.I've done it once, but only because I bought some stuff from Home Depot and it extended outside the rear window, barely past the spare. I left it open and drove home (about a 10 minute drive). I'm sure the window would be bouncing up and down if you're going down a very bumpy road, but I was dealing with all local roads (paved). I didn't see or hear it bump up/down...