swelling in my left testicle

Hi i was wondering if someone can help me. Ocassionally after having sex or masturbating i get some swelling and discomfort in my left testicle. Sometimes it only lasts around 3-4 hours and then goes away. The swelling is around the "cords" that attach to my left testicle and then goes way the next day or in 3 -4 hours. I have also got the pain after surfing a couple of times. The testicle also moves by itself when it is swollen, very wierd.

I am not overly concerned as the pain generally goes away and i am aware that testicle cancer doesn't often involve pain.

It doesn't happen all then time, sometimes i can go 6 months without incident. However in the past month i have had it happen twice.

Any ideas anyone??