Honda Civic Reverse Noise

[Sho]

Right got a problem with my 53 plate Civic.

Everytime i Reverse, there is a noise like a horn being blown . The noise only comes in Reverse.

Iv tested it out in First gear with clutch in letting the car roll back and no Horn noise there. I've even left it in nuetral and let the car roll back and no noise there. So again the noise only comes in Reverse.
The noise last for a while, but quick way to stop it, is tapping the brakes.

Any Idea's? I've never had this issue before.

 

[IAmATeaf]

It's not just the rear pads squealing is it? I get this on my Accord but only when reversing up an incline i.e. when reverse parking the car on my driveway. On flat ground I get no noise.