Welcome to Gaia! ::

If you're describing the noise correctly I would assume (since I can't see/hear it myself) you need a starter. The humm you're hearing is the starter's pinion gear spinning freely and not engaged to the flexplate. The problem would be that the solinoid took a s**t on you, usually replacing the whole starter is the repair unless you can find just the solinoid.

Go under the car and lightly tap on the solinoid with a steel hammer. Sometimes the solinoid just sticks due to corrosion and dirt and you can break it free, but starter replacement is still needed.

LOL dont jump to a starter first. replace small stuff first. check your battery, check main relays and fuses for the starting system. check grounds.