good OP!
speakers need to check periodically(3..10yr), for: cabinets integrity, internal connections deox, bipolar electrolytic capacitors values, inductors, damping material etc..
simplest test is a slow sweep 10Hz..25kHz, starting at low loudness, then gradually increase volume to the max. you will be surprised to hear resonances and distortions caused by drivers and cabinets (cracks in adhesives, lose panels and components). another discovery will be many resonating objects in the listening room (paintings on the walls, glasses etc).