Car making loud whine at idle, very loud on turns. Steering fluid changing levels

Hi, I recently bought a 2007 Toyota Highlander that had just had a full inspection + new rotors + brakes. It suddenly started making a loud whining noise (like a small remote control car revving it’s engine) at idle and while driving, and it gets VERY loud when turning. The sound seems to increase in pitch as I drive faster. checked my power steering fluid, and the reservoir was completely empty! I went to fill it the next day, and it was somehow full to normal levels without me doing anything (kind of brown though)? The sound is coming from underneath the car also. When I checked the fluid most recently, there were some bubbles in the reservoir. The steering is not hard or stiff at all, in fact the steering has felt loose on the car since I purchased it. Is this an issue with a leak in my pump and power steering lines? Does anyone know how I should go about fixing this? And what would explain the resevoir being empty one day, and full the next? I am new to car repairs, every shop near me is booked for the next 30 days so I need to fix this myself. Thank you!

Check your owner’s manual for the proper procedure to check the PS fluid. Sometimes it has to be done after the car has been driven a certain length of time or miles, etc. Squealing noises are often caused by loose accessory belts. My Corolla was making a squealing noise at idle, turned out to be the alternator belt was loose. I expect your Highlander uses a serpentine belt with an automatic tensioner. If so consider both the belt, the pulleys, and the tensioner as possible culprits. It could be the PS pump too. Sometimes I’ll use a length of old garden hose as a stethoscope to isolate where engine noises are coming from.