Phone keeps vibrating repeatedly when plugged in. (LG G5)

I recently purchased a phone lot off of eBay just for fun, and I wanted to test it for myself. When I plug it in (with a USB-C cable), it repeatedly vibrates. The vibration patterns change whenever I unplug it and plug it back in for some reason. Is there any explanation for this behavior?

Clarification Edit: When I plug in the phone, the LCD’s backlight should light up displaying the charging symbol, but it doesn’t appear to do that. Instead, the phone vibrates at random intervals. However, when I hold down the power button, the vibrating stops.

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Maybe a bad connection so it thinks it's being plugged in over and over again?

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Although that’s possible, I made sure to clean the charging port before plugging it in.

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Does it go in all the way flush? And if so have you tried resetting the software?

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It does go in all the way flush, and I have tried resetting the software, but to no avail.

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