Yes it's a Realsense model, I'm not sure about the fan inside/underneath it, I'll check next time I fly,[/QUOT
I'm not saying you did this, but never have the OA switched on when taking off or landing.
There may be something else internally that could cause a sound, but I'm thinking I have not seen reports of any such.
Let us know after you check it out.
Take it slow and easy for awhile, fly in Turtle and Angle modes. Fly in open areas at 100' with the RS OA off and really get familiar with flying it. Make it a habit to hover from time to time and check the ST16 screen readings, especially voltages. The height will usually not be correct if you're close to the ground. Don't worry about the height reading, it's only used to set high altitudes.
You can take off fast but always land slow. get it in a hover a foot or so above ground and ease it down. When it touches hold the left stick all the way back and count to three out loud. (Stay off the right stick). Then ease that left stick back to center and hold the red button down until the props stop. You probably know all this, but I'm just making sure, lol.
You'll be OK. Best of luck.