Noise with ac on
I have started running the air in my truck and when the compressor comes on there is an anoying loud humming noise coming from the inside of the truck. I thought the system may have been low on oil so I drained and recharged the air. The ac blows super cold now, but it is still making the noise. I turned the ac on with the hood open and I can barely hear the noise from the engine compartment. When I get back into the truck I can hear the noise. As soon as I turn the control from ac to vent the noise will stop. I've run out of things to check. Thanks in advance for any help.