I have had this before, its where the hose pushes onto the barb, its because whatever you are using to clamp the hose onto it, is not clamping all the way around, its squeezing onboth sides, but opening a gap for the high pressure water to spray out. I have used the O clip things but didnt like them much, i used the smallest jubilee i could find, but they may not be still in the right circular shape when tightened up to make smaller, so use some pliers to bend the jub clip round again before tightening. Also i would wrap ptfe tape thick around the outside of the hose where the jub clip would tighten on so it cushioned the hose and stopped the same thing happening.