How to determine problem in blower motor in a 1996 Chevrolet Cavalier?

Check and see if the blower motor is secured to its housing as I've seen twice in the past. The mounting bolts/ screws were missing, the motor getting loose and the blade rested on the case and quit turning after making noise.

You will find this out when go straight to the blower motor's connector and check to see if you have power to the connector.. If you have power then the motor has died. Replace it.

Always Start with The fuse then work your way up to the resistor which 9 times out of 10 that's what it is. its highly unlikely a relay has gone out but there there not completely invincible. if it any of those check the heater switch and connect behind the dash, the connectors tend to overheat and melt. if all these are ruled out the motor has taken a crap on you and you need a new one. but make sure there's nothing big that was caught up in your fan and just wrapped itself causing a jam inside.

Agree with Fred rattling and then the motor likely locked up or jammed. possibly blowing the fuse as a result.

The rattling sound is the motor. It could also have blown the fuse , which should be located in the fuse block.

A bad control or bad fuse does not cause rattling.