you won't hear the oleos extending, as they do so reasonably gradually as the aircraft takes off. neither will you hear the bogie tilt gear, as they are hydraulically locked, and by the time the gear is right off the ground, the wheels are all the way back.
the 2 distinct sounds you can hear are: 1. the gear locking into place in the uplocks (under the floor) and 2. the doors slamming shut behind them - especially on a 747/767/757, where the main (wing and body for 747) doors are hydraulically opened and closed, independent of the gear. the 767 ones especially close with a bang. next time you're spotting, watch the 76 doors open, then the gear raise, then the doors close behind.