Insist dealership check vehicle under the exact same conditions

In another thread, I described that our truck has been doing a deep rumbling noise at certain speeds when the trailer is connected...it only happened under those conditions....no noise when driving without the trailer

To try to duplicate, the dealership service rep put some amount of weight in the bed...he didn't sense any issue...tried to tell me, 'there's nothing wrong'....I didn't accept that

Once he hooked up to a trailer similar in weight to ours, the problem surfaced....now they've replaced the driveshaft

The point: it's important that, if a problem only occurs under certain conditions, that we insist the repair tech duplicate those conditions in testing