New Years day I went out in the garage to smoke a cig and noticed a hum coming out from under the rear wheel well. It was an electric hum. I thought it was the rear tailgate latch hung up but that wasn't it. Then I put the key in and turned it to the on position and then back off. The hum went away. I'm beginning to think it was something like a pump in the tank stuck on. Anyone else had anything like this happen?