loud "thud" while braking in reverse

[harmankardon35]

As the title says..... It's not when i engage reverse gear, but while im moving in reverse and i hit the brakes. I did a search, and possible solutions were either the brake calipers are loose or the slip-yoke needs greased....Any other common problems that may cause this? The thunk is quite violent, it would make any other person think they backed into a brick wall with the noise it makes!...Any comments are greatly appreciated!

thanks in advance...:roll: