heres the problem when the clutch is not pussed down there this loud clicking noise coming fromthe tranny but when its pressed down it goes away i thought it was the throw out bearing so i changed it but it wasnt now im thinking it the mainshaft bearing but not sure does anyone know what it is

 

did you check the springs on your clutch disc when you changed the bearing? because my buddies did the same thing and we changed both pilot and throw out bearing and it didnt stop and we then looked at his ckutch disc again and realized the springs on the disc were stuck so the disc was shot... replaced the clutch and everything was fine...