Is this a steel line? Is it rusty? This is very common on old rusty hydraulic lines, brake lines and fuel lines. They get rusty, sometimes only in one hidden spot covered by a clamp or behind a cross member. Or sometimes they are rusty all over. But they are on the verge of blowing out a rust hole. The only thing stopping this from happening is a scab or rust flake, or the last paper thin bit of sound metal. When you disturb the line suddenly it starts leaking or in extreme cases, snaps off in your hand.

This is so common that nowadays if I have a leaky brake line or hydraulic line I never try to fix it, I replace it and check and replace every other line in the system while I am at it because I know they are going to blow as soon as I fix the first one, if they are anything less than perfect.