06 Sienna rattle

I have an 06 Sienna LE with a rattle that is driving me crazy. I have 43,000 miles. The cowling was bad and replaced at 25,000 miles. Now I have a metallic rattle in front drivers side. BUT, it only rattles at 40 degrees or below, with some wind, and at interstate speeds, usually 55-60mph. Occassionally it will rattle at lower speeds when it is really cold. The rattle was noted by the dealer before 36,000 miles, after numerous trips. It had been in several times and they never could hear it, but they can't seem to figure out what it is. They're not too interested in figuring it out either in my opinion. My problem is that I spend about 11/2 hrs. per day on the interstate and I hate rattles. Can anybody help me????