I don't know your trailer. But, if the pump is not accessible from outside, it is probably behind a panel in one of your cabinets. The back panel in many cabinets are intended to be removable, may need to undo a couple of screws. I've also heard of them being under a bed. It will not be inside the sealed bottom.
Hopefully, someone with your model trailer will chime in with a location. Do you recall where you heard the pump when it was running?
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