Does your rear PDC beep randomly? I always thought it was water dripping over a sensor, but now I'm not so sure? 

Your rear PDC is only supposed to work when in reverse, i think, if it is beeping while you are in drive there may be a problem some of my Previous cars
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True - it turns on when put in reverse but stays on until the forward speed exceeds 5 or 10 mph. It's beeping when going forward (until it turns off) - that's what made me think of water drips, but (a) today is dry, and (b) why doesn't the front do it when going backwards? 

I was under the impression that as soon as you selected drive it turned the rear sensors off, but you are right above 15mph the sensors are turned off anyway, Come to think about it you are right when reversing the front sensors stay on as well.

If yours are sensing something that isnt there its either a ghost or a fault some of my Previous cars
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Have you got this done...?

Technical Service Bulletin No.LS413-002
19 July 2006
Subject/Concern: Range Rover Sport - Front Parking Aid False Warnings
Models:
Range Rover Sport
(LS)
Vehicles with front parking aids
Vehicles with front parking aids VIN-range:5A900109-6A960177
Markets: All
Section: 413-13
Summary:
A customer may report a concern that the front parking aid system sounds unnecessarily.
Cause: The current system strategy means that the front parking sensors will operate when a
forward gear is selected following reverse. Sensor operation is canceled when the
vehicle speed is above 10mph (16kph) but will operate again if the speed drops below 10mph (16kph). This can give instances of sensor warnings when the vehicle stops at a junction and another vehicle or pedestrian passes in front of the vehicle, resulting in the above complaint. This is not a fault with the parking system, however, an alternative system strategy is available so that the system operation is canceled when the vehicle speed is above 10mph (16kph) and will not operate again until the vehicle speed is below 10mph (16kph) and the fascia front parking aid switch is selected (or until a forward gear is selected following reverse gear selection during parking).
Action: On a customer concern basis only regarding the above, refer to the Service Procedure
detailed in this bulletin to renew the parking aid system control module. The new
system operation must be explained to the customer.
NOTE: The new software strategy is contained within the new control modules below and is installed to vehicles
from the closing VIN above.
Parts Required:
Description Part Number Quantity
Parking aid control module YWC500550 1
Labour Time: 0.40 hours
Operation Description Operation No. Time
Parking aid module - renew 86.54.10
Repair/Claim Coding:
Causal Part: YWC500313
ACES Condition
Code:
42
Defect Code:
Service Procedure
NOTE: The new system operation must be explained to the customer. Malaysia Boleh!
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It's better this way [ I had mine updated to this sequence ] as previously it always triggered false alarms from the front PDC when in slow moving traffic or if pedestrians were close by in town traffic etc etc.

So having had it converted to the latest set up with new module - I now get the same beeps from the rear when turning around in my drive - I too thought it was poss/water/rain etc but like you say..... get to 10mph and it switches off & the front will not deploy untill you now engage in a parking situation selcting reverse etc. If I was to drive at something with the front now dormant......... and pull up towards a wall for instance... it wouldn't sound unless I switch it on manually = much better.

As for those false rear beeps..... maybe its a case of fine tuning the sensor at the rear, perhaps I/we should enquire at the dealers ???? 
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