What gen is your accord? I have this type of issue on my 5th gen. When ever back up and slow down put the car in drive or reverse there is a slight popping noise up front. I took it to honda on this and they said it is a normal sound and it has to do with the brake pad boots (term???). The piece that goes around the disc. (Sorry for the illexpresions) Honda said it does that because the boot moves higher or lower depend on drive IE Drive or Reverse. I don't know if this is true it is just what they told me. I have never had any problems with my brakes going out or wearing excessively fast.