What causes throbbing in the testicles?

Many things: Many things can lead to achiness, even pain. Of course injury is one cause. Men can develop low grade infections in the testicle, epididymis causing pain. A prostate infection is common as well. Other causes include hernia, and varicocele. Occasionally a mass/tumor can be the cause. A careful examination of the testicles, groin and lower abdomen is needed to better determine the cause.