clutch problem or not?

[n240sx]

Yesterday i was breaking in my engine for a little while, the car would just stop accelerating for a split second, but it was a violent and jerky split second.there was also some type of clunking sounded involved with it, but i can't remember exactly what it sounded like since i guess i was in a small state of shock. it did it two more times on the same run, and i decided to take it back home. i let it idle when i got home, and there was a knocking/rattling sound coming from the tranny only when the rpm's would get lower than ~700 rpms (i have a slight idling problem), but i'm just assumming that this can be written off as the clutch chatter that i've heard so much from others with the clutchmasters stage 5. also, the sound goes away if i disengage the clutch.
After i diagnosed the problem, i took it out for another couple of quick runs with plenty of short burst and decleration, and there were no problems whatsoever (the clutch engaged/disengaged just like before). the only issue that i have is that the clutch area made no noises on my previous runs, so i think it's kind of odd that it would just pop up all of a sudden. btw, the motor is a forged bottom end 93 KA24DE that doesn't even have 10 miles on it. thanks