Step 1: Find a Toy Guitar
Step 2: Unscrew All Screws
Step 3: Open Up Guitar
Step 4: Find All the Circuit Boards
Step 5: Lick Your Fingers and Touch Soldering Joints to Experiment With Weird Noises.
Step 6: Once You Find the Weird Noise You Want It to Make...
solder a wire on each of the solder joints that make that sound