Awesomedog loves tennis balls because they make a squoosh sound when he bites them very hard. It's a perfect combination of two of his favorite activities: biting stuff and making noise.
Kong makes squeaky tennis balls. Once in a while I let him have one as a special treat. A squeaky tennis ball only survives about 15 minutes of nonstop compulsive squeaking before it gives out.
Awesomedog has some obsessive-compulsive tendencies, this is why he is not allowed to play with laser pointers or flashlights. One of the things that sets off his OCD is things that make noise. Tennis balls and squeaky toys are definitely high on the list, but sometimes he'll settle for anything that makes noise. Loose cabinet doors are a favorite.