There are two instances when rattling noises are most concerning. If you hear rattling or loud banging noises from inside the system, it may indicate that something in the motor or blowing assembly is loose and needs tightening. It is wise to turn the system completely off and have it repaired before anything breaks completely.
Another place you may hear rattling is from the fan in the compressor unit when you are turning the system on and off. Unlike the clicking noise, this is a sure indicator that something is loose in the hardware of the fan or the motor is failing. Additional noises such as humming or screaming may indicate that the capacitor is starting to fail. In these cases, you must call a professional technician like 212 HVAC to come and fix your HVAC system immediately.