Sorry if this has been covered but have not found an answer in my searching this forum the manual or the google.

About 2 weeks ago, my 2021 RDX A-Spec started playing exactly 5 sharp beeps, every time I start the car, it begins about 3-4 seconds after the car is running and the dash is booting. No lighted indicators/warnings on the dash display. I have just turned 10k miles and my oil is at 40%

 

here's a vid

 

Could it be the blind spot alert? Double check the light on right or left lighted alert. If done in a garage, for instance, the alert may be due to pickup of the garage structure or something IN the garage. Try it outside when no obstructions are in evidence (If not already done).

 

That would only alert you if you were using your turn signal. When I back up with my parking sensors on, you just get a steady beep.

The only time I get 5 quick beeps is when I leave the car running and step out of the car and close the door. Perhaps your fob is on the fritz? But it will also give you an error message that the fob is not detected.