Sounds like the compressor clutch is cycling on and off .
Need you to check this because if the compressor is not cycling then it could be the compressor itself .
We have just changed one for the same problem on at idle would click internally and after getting over 1000rpm would stop .
So at idle lift the bonnet and check the compressor clutch each times it clicks should stop then start turning this you will see .
If does not do this then possible compressor failure .
Remember i am not there to hear see or check I'm only going on experience so you need to check and if the sound is coming from else where let me know .
Still need additional information then please get back to me with the reply button, and not the poor or bad service, this way i can get back to you or suggest another expert if needed.
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Kind regards Greg.