Hello All. I have a S320 LWB 2001 . i have noticed that when driving 30mph or over, An air compressor kicks in, And sounds to me that it is running abit rough, however, When bring the car down to under 10mph the compressor turns it's sell off. And i dont think that the compressor comes on everytime i go over 30mph. Can anyone help me with this ?? What can i do ?

Any advice is welcome