My trailer is giving me a rattle I can't figure out. I'm newly towing a 2003 Jayco QWest tent trailer with a 2007 Sienna. I've towed it a couple hundred miles already. On the road, at over 50km/h (30mph) the trailer has a rattle that can be heard inside my van with the windows up or down. It almost sounds like something is tapping on the roof of the trailer, but I can't figure it out. I've over-secured all the possible suspects, just to rule them out (hitch assembly, propane tank, stairs, support arms, anything not tied down inside). Anyone ever encountered this??