Hello, I have a 2011 Silverado with 5.3 engine and was hoping someone has heard of my issue. I have a whistle/howling coming through my vents only when the air condition is on. It will make this sound in either park or when driving. It does not happen during idle but only around 1000-3000 rpm's. In park, I can get the whistle to hold constantly at 2000 rpm's and immediately will stop when I disengage the A/c. While driving, the whistle will start and continue throughout acceleration up to about 3000 rpm. Any help would be greatly appreciated!

 

one possibility...... happened to me on a dodge Durango. the refrigerant level was low. filling the system accurately, fixed the problem.

 

Low freon caused the A/C lines to vibrate and cause the whistle noise. Serviced the A/C system and sound is gone! Hopefully there isnt a leak!