02 transmission

i have an '02 malibu with 51,000 miles. this week i've started having trans problems. when gears are changed it makes a loud noise and kinda pops. there is even a little jump when put into rev. and drive. it's not as bad when the car is already in drive and switching gears as i go down the road. i'm completely stupid when it comes to car stuff but, it is my understanding that my trans is "a nonservicable unit". that's what the precision auto guy told me today when i took it in for an oil change and to have the fluid checked. he said that i may need a new transmission. please help me!!!!!