Strange lump, but doesn't stay in one spot.

[TheVai]

Lately i've been noticing a lump on my testicles, but it doesn't seem to stay in one spot. It feels like it's on the testicle, but i've felt it on the very bottom of the right, very bottom of the left, and the very top of the upper left. Sometimes I can't feel it at all.

I'm thinking it could be a certain vein or something that has to be there, but i'd rather be safe than sorry. Can anyone maybe give me some insight? Thanks a lot. Any help is greatly appreciated.