Why does it sound like my jaw is breaking when i bite down on an old crown? not loose/feels ok.

Loose: It may not be loose on the surface but a crown goes deeper which may be cracked and not visible.

Hard to say: It could be a problem with the crown, or the substructure of the crown, or the tooth itself. Or it could be a grinding sound coming from the joint (tmj). Either way you should see your dentist to evaluate, determine the cause, and discuss your options.

Jaw or tooth problem: It could actually be your jaw joint or a cracked part of the tooth in a spot you can't feel. I would recommend having an exam just in case there is a significant problem.