Sound waves and the Speed of sound on an Aluminum Rod másolata

If I hold a rod of a solid material in my hand at the ½ way point and stimulate it "properly", it will start to vibrate and produce sound. "Properly" means that the stimulation causes the rod to vibrate at its resonant frequency. If you hear a sound, you have done it "properly".
What part of the sound changes with more nodes? What part of the sound changes if the length of the rod changes?