Can someone explain what this is plz

[Joshua1972]

Hey,
Thought I'd seek some help plz and this is cheaper than a doctor lol
Ever since i was a kid when I went swimming I felt like(no joke I swear-I'm 17 now) there's like some sort of ******* microchip going around in my head!
Obviously it's not a microchip.. But that's the best way to explain it... I never  get any headaches or anything, just as simple as when I am swimming( and at the beach going into waves and stuff underwater, Never feel it when I'm not in water) there is something going moving in my head.. Like a piece of metal.
You know when you are underwater and all sound is kinda blocked off? I can hear the  thing moving inside my head like a little piece of Tin (I can't actually feel it colliding into anything I can just hear it and feel it move if that  kind of makes sense lol...)
I come here because it happens again(I haven't swam in like 3 years no joke-last time it happend) and a kid at my school recently for having some sort of brain problem evident since birth that just started causing trouble and was unnoticed...i.e why I thought this might be noteworthy to ask lol
Again it doesn't hurt or anything, it could be as simple as water maybe moving around in my head or something idk?
Thanks for your help! (Might want to add I'm an extremely healthy and fit guy---> lean muscle  wise not so much with cardio.. Eat healthy and yeah.. Again I've had this since I was like 6...
Thanks again!