Symptoms: Motor like noise from wheels and poor fuel economy

Packed the car tight and got on the highway. After that there is a sound that sounds like it's coming from the front wheels like an outboard motor and my fuel economy has jumped 5L/100K's. I start to hear it at 45 kph and it just gets louder. It's probably not an engine/revving problem because it's the same level of noise whether I'm coasting at a speed or accelerating at that speed. Any idea what the problem is? I also think there's a kind of vibrating from it too.