Britdog15

i have a 98 gt 5 spd. I was driving home from work and i shift to 3rd and it was at about 1300-1500 rpm in 3rd gear. when i gave it some gas there was a single knock from what seemed underneath the car. So i let off the gas and then gave it a little bit and it did it again. I tried this again to see if it would persist and there was no noise. Do you have any idea? I'm a little worried because my buddy said that the tranny in my car was produced by a company being merged or bought out or something like that and that the quilty is horrilbe because they did 2 years of production it 6 months. and that he had his rebuilt with the new companys parts because they are better quility. thanks everyone
oh and the car has 104000 miles and the motor is rebuilt with about 1200 miles on it