that is a DC 'breaker', otherwise known as a high-amp resettable FUSE... generally inline between high amp devices that require a lot a 'sudden' power. I imagine yours could be the fuse link between the Solenoid and the Latching Relay for providing Chassis battery charging from Shore or Generator power, after the House batteries have reached a certain level, etc. The 'whirring' noise could simply be the solenoid 'powering up' when the power was reestablished.
You may not be seeing any 'strange' electrical behavior simply because your Chassis batteries didn't need any charging, so nothing seem 'amiss'...
that's just a guesstimate, since you won't know unless you trace these wires back to their termination points...
'14 Palazzo 33.3 bunkhouse 34' diesel
KingTailgater2 Dish HD, 100w/5a SOLAR, BlueOx
100,000+mi since '14 - US, Alaska, Canada.... formerly Georgia, then NorthCarolina, now Alabama : )