Test for power at the soleniod wire (one hooked up with 8mm) on the starter when you turn the key. I think you are getting it, but it's in front of the engine and your sound is coming from the wrong places.

If you get power with that...then it's either a battery/cable not supplying enough power to the starter, a locked up motor, or possibly a bad ground.

You said you checked the ground at the body. On the front lower trans stud is the main ground for the engine.