Just like some lawnmowers or other small engines can interfere with a radio or TV signal, a running vehicle can interfere with your keypad signal. It is not as common since most car and garage door opener designs devote a lot of time and resources to finding frequencies that will cause as little interference as possible, but it can still happen.
It could be there is something that needs adjusting on your vehicles, or you may have an Onstar system or built in factory remote that is causing interference. Since you have the same problem with multiple vehicles it may also be a problem with the keypad or the opener itself.
Unfortunately, it may be pretty difficult to solve the problem unless you have a professional measure the interference with a frequency meter to determine what options for repair there are. Your Manage My Home profile was not completed with any model information so it is difficult to provide any specifics but your opener or keyless may require an adjustment or a component replacement to correct the problem.