If you notice some strange noises coming out of your air conditioner then it is a matter to be concerned of. Such noises clearly indicate that it is time to call for professional help. You can diagnose the problems by your own by understanding the right causes for the noise. If you find out unusual sounds coming out of your cooling and heating unit then try to find from where exactly the noise is coming from. If you are hearing it come from the duct work then there are chances of the ducts being damaged. If the sound is coming out of the air handler or the blower then there is possibility for an air leak. If a sparkling noise is coming out of the refrigerant pipe then the problem will be a leak of the refrigerant which needs to be repaired immediately by a professional.
Another unusual sound that needs immediate action is the sound that comes from the electrical panel. It could turn out to be dangerous if not attended immediately. If the problem is with the thermostat then there would be a clicking sound. If the indoor air handler has got a problem then a squeaking noise will be heard through the ducts. If a moving and scratching sound is heard through the duct then some rodents might have entered your duct and will be living inside. If rattling noise is heard then some parts of the unit might be loose and need to be tightened up. A loose fan blade can make the rattle sound; try to get it tightened by a professional.