My rear parking sensors have an intermittent problem they sometimes work other times they emit a series of short beeps no matter how far away an object is

Three ideas here Charlie. Tyre pressure sensor, low key fob battery.

https://www.google.com/search?q=2017+Chevy+Impala+has+recently+started+to+emit+a+series+of+very+quick+beeps+when+exiting+the+car

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you can check the sensors by putting in reverse with ign on no engine running. and listen to each sensor in turn put your ear close to sensor it should click very faintly any that don't are poss faulty does the sounder emit a error tone one long beep if not check for water in the module located in boot against rear panel.if that's ok the sounder may have gone down

The parking module is in the boot to the left hand side under the floor. They are prone to damage by damp. pull all the plugs off and spray WD40 all over and refit/remove the plugs a couple of times - sometimes leaving the car in a warm dry area for a while with the boot open so all can dry out often brings these units back to life. Failing that get power checked to the module and to check sensors listen to each sensor - if it is working you can hear a clicking sound from it. if all above fails - it might be new unit time :-(
hope this helps - good luck.

Check the system for DTC'S - diagnostic trouble codes should be the first step in the diagnostic process . Then reading factory service repair manual how the system works , viewing wiring diagrams .
Object Detection Description and Operation
Ultrasonic Rear Park Assist Operation
The ultrasonic rear park assist system senses how close the vehicle is to an object. The distance is determined by the 4 object sensors located in the rear bumper. The object detection system will notify the driver when backing up at speeds less than 8 km/h (5 mph). The object detection system will use the rear parking assist (RPA) display and the radio speakers for notification.
When the ignition is ON and the vehicle is placed into reverse, the object detection system performs a bulb check. During the bulb check, the 3 indicators on the RPA will illuminate for approximately 2 seconds to indicate that the system is working. The object detection system performs a bulb check and operates when the following conditions are present:
• The ignition is ON.
• The vehicle is placed in REVERSE (R) for rear parking aid.
• The vehicle speed is less than 8 km/h (5 mph). At speeds greater than 8 km/h (5 mph), the object detection system is disabled. The red indicator flashes to warn the driver that the object detection system is disabled.
The object detection system senses how close the vehicle is to an object. The distance is determined by the 4 object sensors located on the rear bumper. When the system detects an object, one of the following will occur:
• If the object is less than 0.3 m (11 in) away from the vehicle, the amber outside, amber middle, and the red outside indicators flash and the chime sounds continuously for 3 seconds.
• If the object is less than 0.3-0.5 m (11-20 in) away from the vehicle, the amber outside, amber middle, and the red outside indicators are ON.
• If the object is 0.5-1.0 m (20-40 in) away from the vehicle, the amber outside, and the amber middle indicators are ON.
• If the object is 1-2.3 m (40-91 in) away from the vehicle, the amber outside indicator is ON with a single chime when the object is first detected.
Object detection system can detect objects 7.6 cm (3 in) wide and at least 25.4 cm (10 in) tall. It cannot detect objects above the level of the roof.
If the object detection system detects a malfunction, a diagnostic trouble code (DTC) will be stored and the object detection system will send a serial data communication message to the instrument panel (I/P) to SERVICE PARK ASSIST message on the driver information center (DIC). Then the chime will sound and the red indicator on the information telltale center will be lit continuously. The red LED in the rear display will be lit, notifying the driver that a malfunction exists. Message will clear once the driver acknowledges it.
Each object sensor is a three wire sensor that is both a transmitter and a receiver that comprises a signal circuit, a low reference circuit, and an 8-volt supply voltage circuit. The rear object control module supplies 8 volts to the object sensors via the object sensor supply voltage circuit and provides ground via the low reference circuit. The rear object control module triggers the sensors in a sequential loop and after each sensor transmits, the rear object control module uses the echo or signal return to calculate the distance and position of an object from the rear bumper. The rear object control module directly controls the RPA display.

Do you know what DTC'S are ?
DTC B0958 01: Parking Aid Rear Sensor 1 Left Corner Circuit Short to Battery
DTC B0958 06: Parking Aid Rear Sensor 1 Left Corner Circuit Short to Ground or Open
DTC B0958 08: Parking Aid Rear Sensor 1 Left Corner Circuit Signal Invalid
DTC B0958 21: Parking Aid Rear Sensor 1 Left Corner Circuit Incorrect Period
DTC B0959 01: Parking Aid Rear Sensor 1 Left Middle Circuit Short to Battery
DTC B0959 06: Parking Aid Rear Sensor 1 Left Middle Circuit Short to Ground or Open
DTC B0959 08: Parking Aid Rear Sensor 1 Left Middle Circuit Signal Invalid
DTC B0959 21: Parking Aid Rear Sensor 1 Left Middle Circuit Incorrect Period

DTC B0967 02: Parking Aid Switch Circuit Short to Ground
DTC B0968 00: Parking Aid Indicator Circuit


Your best bet , take it to a qualified repair shop.

How do you know it's a sensor problem ? DTC - diagnostic trouble code ? Take's professional type scanner to read these DTC'S
DTC B0958 01: Parking Aid Rear Sensor 1 Left Corner Circuit Short to Battery
DTC B0958 06: Parking Aid Rear Sensor 1 Left Corner Circuit Short to Ground or Open
DTC B0958 08: Parking Aid Rear Sensor 1 Left Corner Circuit Signal Invalid
DTC B0958 21: Parking Aid Rear Sensor 1 Left Corner Circuit Incorrect Period
DTC B0959 01: Parking Aid Rear Sensor 1 Left Middle Circuit Short to Battery
DTC B0959 06: Parking Aid Rear Sensor 1 Left Middle Circuit Short to Ground or Open
DTC B0959 08: Parking Aid Rear Sensor 1 Left Middle Circuit Signal Invalid
DTC B0959 21: Parking Aid Rear Sensor 1 Left Middle Circuit Incorrect Period

Could have other codes
DTC B0967 02: Parking Aid Switch Circuit Short to Ground
DTC B1008 42: Calibration Data Not Programmed
DTC B1E3A 03: Sensor Power Circuit Voltage Below Threshold
DTC B1E3A 07: Sensor Power Circuit Voltage Above Threshold

There are a lot of other qualified repair shop's besides the Dealer .

Sometimes sensors can just be dirty, try wiping them with a clean soft rag.

Try to clean rear parking sensors. Check also electric cables and connections, clean if necessary. Commons faults are sensors out of order. If one or more sensors faults you hear only a continous constant noise when you put in "R" gear. You need a VAS, VAG-COM, Bosch KTS, ... diagnosis scantool. The factory parking system will be scaned from errors with this instrument, and you will find exactly which sensors are out of order (for example: rear left center sensor, rear right side sensor break off, short to ground or short to plus).

Try to clean rear parking sensors. Check also electric cables and connections, clean if necessary. Commons faults are sensors out of order. If one or more sensors faults you hear only a continous constant noise when you put in "R" gear. You need a VAS, VAG-COM, Bosch KTS, ... diagnosis scantool. The factory parking system will be scaned from errors with this instrument, and you will find exactly which sensors are out of order (for example: rear left center sensor, rear right side sensor break off, short to ground or short to plus).

You need to have the transmission serviced. Make sure you tell them this problem. It is a solenoid problem in the transmission that will need replaced.

Well you can find manual here on the site, mechanic shop (it costs usually 8$) or on your library too.