It's much harder for you to monitor the quality of the TX signal sitting in the aircraft. If its a coax / connector problem then it will be there during TX, and its a lot easier to check for problems by checking VSWR of the installation. My starting point would be to remove the radios from the rack and plug them back in, you may be surprised, often operating the connectors is enough to "cure" the problem. As is a spray of good quality contact cleaner.