It may be that your condenser coil is chocked or that your filter is dirty. The coil which is located at the outdoor unit has a number of countless cooling fins like the ones that are in a car radiator. All these fins have a high probability of accumulating a lot of dirt and debris. When this happens, the best thing to do would be to call in a qualified and skilled technician to have a look at your air conditioning system. You may end up paying around $75 to $150 depending on how serious the problem is.
* Hearing of weird noises when your air conditioning system is in operation or when it is starting up
Even though there may be a serious problem, the cause of this noise may be a screw that is loose.