I experienced a noise sound very similar to the one you described, and it took a while to figure out and it turned out to be my sunglasses sliding back and forth in the overhead bin.
I did a 55-mile mpg test with my 6th generation SR5 (52 miles of highway / ~3 miles of stop & go). I got 27.5 mpg. The cruise control was set on 70mph, several hundred feet above sea level, no wind, ~80 degrees and the air dam attached. I verified this by the gas being topped off before and after.
If anyone is concerned about gas mileage, I did a 55-mile mpg test with my 6th generation SR5 (52 miles of highway / ~3 miles of stop & go). I got 27.5 mpg. The cruise control was set on 70mph, several hundred above sea level, no wind, ~80 degrees and the air dam attached. I verified this by the...