I had the same problem with my 99 SVT contour w/ 70k miles. I thought it might be the power steering since the humming sounded very similar to the whine of the steering during full wheel turn. It was not the steering...It is progressively getting worse and more frequent. Used to happen when the car was first started now happens during a drive at all speeds although it is more constant at idle when there is a power draw such as the power steering or A/C - defrost. I am wondering if it could be the battery. It is the original and I dont drive the car more then 2 or 3 times a month (garage baby). I do start it every week for 20 minutes but last drive I turned on the a/c while cruising at 30 and the car stalled. Anyone think the humming noise has something to do with the battery and lack of power???