The next test we should run is to take a video of the cavity without any power applied over a five minute duration. We should then initiate a 90 second run and see if the cavity moves during that time only. After the test, we will take video for another five minutes. If the cavity only moves during the 90 second test run, we can be safe in saying it is because of the power applied. We also need to put a cowling on the shelf containing the fan in order to eliminate air movement.
As for heating the cable, how low can we drop the temperature in the lab? I know there is a temperature control at the entrance and can we cool the lab down to 5c and run the tests again?