HVAC Whistle

[Abatk601]

I'm having an issue while my A/C unit is running. Periodically the line-set going to the indoor air handler whistles. The whistling sound last for only a 5 to 10 seconds then repeats again and again every 40 to 45 seconds. It is typically louder during the compressors startup then gets progressively quieter as it continues to cool the house. Other then the whistling sound the A/C runs fine. The unit is 4 years old.
Any ideals on what could be causing the noise?

 

[bazar01]

Check the system pressures. If the high side is a little high and the low side is a little too low, you have a foreign object in the flowrator or metering orifice. It could be obstructing the refrigerant flow thus making the noise but it is not completely blocking the opening which makes the system still work outside the optimum design pressures.
To open the metering orifice located inside the indoor unit, you need to pump down the system, open the orifice, remove the blockage, vacuum the system, then release the refrigerant from the condensing unit.

 

[bonneyman]

Breaking into the system would be risky if you're not thoroughly familiar with all that needs to be done and have the proper equipment. The system should have a 5 year warranty (at least) on the sealed system portion. If I were you, I'd call the installing contractor back (if you are the original owner) or a competent HVAC contractor. I'd hate to see you try and DIY and not properly evacuate or something, and void your warranty.