2009 Marquis noise coming from driver side cabin, can't figure it out!
 

Need your help please! I have a 2009 Marquis with 55k on it. It has this weird noise that comes from inside the driver side cabin. It sounds as close to a dog whistle. It can be heard all the time, idle or driving and ONLY goes away once it hits exactly 1,500 RPMs or higher. It also doesn't matter if I have the HAVC on or off. It's driving me crazy! Any ideas on what it could be??