I am 24 years old and I have discovered that I have a hard lump at the lower part of my left testicle that comes and goes. During most time there is nothing really there, but when I get an erection it almost always shows up. It is about the size of a small grape and is very firm. There is no pain or tenderness, it just appears and after I ejaculate it disappears, not immediately, but it does go away. I am worried that it might be testicular cancer but there is no pain or any ill effects. I was interested in what might be happening.