If the fat used for frying is at the appropriate temperature for your cut of chicken, it wll sizzle as the chicken is submerged. That's caused when the chicken begins to shrink and push moisture out into the hot fat. You'll see tiny bubbles at first; as the chicken cooks, the bubbles get larger. If bubbles disappear completely, most likely your chicken is overcooked. 

When fried foods of any sort sit in grease that isn't bubbling or sizzling, the food is soaking up the fat. That's where really greasy fried food comes from.