BMW Repair: e39 knocking, mid nineties, engine compartment

Question
I have a 1999 528i (BY23643) and recently it has started to develop a knocking sound coming from the engine compartment. At first I thought it was the engine itself as I has done an oil change not long ago. The knocking has become more frequent and louder. I now believe it has something to do with the air conditioning as it stopped when I turned the a/c off. The temperature has been in the mid nineties the past couple of days. Could this be a contributing factor???

Answer
Mike, noises are hard to diagnose of the internet, but it may be the A/C compressor is failing. Price it out as they are expensive. If you do replace the Compressor it is advisable to replace the reciever/dryer unit on an older car such as this aswell.
-Evan