The gentleman answering the door at the apartment party is none other than Tom Williams, associate producer and Jack Webbs right hand man. He makes a few cameos in Dragnet and Adam12.
The electronic sounding stock music used often in the early seasons of the show to indicate a disturbance of some sort is used here when Malloy and Reed approach the Hewlitts' unit on a disturbance call.
415 = disturbance.
484 = theft.
Code 2 = urgent, no lights or siren.