clutch/tranny questions

Hey i just purchased my s14 zenki today from TINC (real nice guy) and so i just wanted to see what it was capable of. So me and my friend tried were just fooling around and then when i came to a full stop I rev it appropriately to maybe 1.5k -2k and for the first second i feel a rattle in the clutch or tranny. It feels as if i didnt give enough gas or it felt like i started in 2nd gear but i didnt…It only happend for the first second then all the other gears were fine. After maybe 10min i try again at a full stop. It isnt that bad anymore but still there. Anyone have any suggestions? On another note…i did it by mistake and have never done it…but i was goin maybe 50km/h and i put it into neutral…and for some reason by accident i clutched in and put it into first…or at least tried to…it wasnt in gear yet casue i was till fully on the clutch but it grinded…is this supposed to happen? First time i did it and i just wanna know if thts suppose to happen. Thanks!

ya if your moving at a decent speed it will grind if you try to put it in first