Usually metal tubes are rigid and affixed to things that don’t move. Rubber lines are used on either end of a metal tube as the go between connection between the rigidified metal line and things that move, like engines or engine mounted compressors.
If the wrong type of hose is used, or if the hose is shortened during fitting replacement, especially hydraulic type hoses, then they get stiffer and more rigid. Between the transmitted vibration and the movement of what ever the hose is connected to, there is a lot of stress put on any and all fittings of the hose or the rigid metal lines and associated fittings the “flexible” rubber line is connected.
I would take a look at your flexible line lengths and make sure your using the most flexible rubber line rated for the pressure of your system. If possible, make the line longer do you can put a loop in it - but you don’t want the loop tight or it will transmit vibration (vibration is what is causing your issue in the first place).
Maybe look art a different set of fittings at each end of the rigid metal line that would insure the rubber line can minimize transmission of vibration.