Issue with rear parking sensors

My rear parking sensors do not react to near objects anymore. Instead they beep twice every two seconds from the moment I shift to R. When I shift back to D, P or N, the beeping stops. Any thoughts?

Jet washer used? Try gently blowing them out with an air hose or hair dryer maybe and see if it helps?

Interesting thought.....

I had brought it in for service and a little bit of body work. After doing their thing they called me and said "when backing out of our garage, we noticed the rear sensors were not working well". I had never noticed it. Wheat I did notice after picking up the car, was it was cleaned by them. I happen to know they have an indoor washing location. Maybe they meant backing out of the washing location .....