Squirrels are chatty animals. Ask anyone who spends time around the rodents and they tell of rapid fire chattering and staccato calls coming from the critters. A good squirrel call is one that creates a fast and repeating click. Two quarters clicking together in rapid fire action is a good starting point to fashioning your own squirrel call. Success is determined by attracting the animals to your call, and not every group of squirrels responds the same. Start with a basic formula for the call and experiment.
Cut out two pieces of cardboard the same size as the diameter of the PVC tube.
Duct tape one of the cardboard circles to the end of the PVC tube and place either two quarters or two steel marbles into the PVC tube. Tape the other cardboard end to the small tube. If using the steel marbles, push one or two small foam packing peanuts into the tube as well.
Shake the tube to create a rapid fire chattering sound, much like the squirrel when scolding from a tree branch. Experiment with the speed of the shake, or the materials on the inside of the tube. Try one quarter and one steel marble or other such combinations to get the sound and speed the squirrels respond to.