not powering on, wierd vibrating and short sounds...

So...

I bought almost new nexus 5x from a friend that jumped into a sea with the phone in his pocket. I don't know how long it was in water but after teardown, salt was all over the place. I have already done the water damage process and also removed as much salt as I could (dissolving everything in distilled water).

So the problem is that when I try to power on the phone, it makes a short "vibrating sound" and if I hold the power button, that sound repeats but only once per hold. If I just click the power button, it makes a "shoe sound" - like someone would step on the hard floor with a high heel. Oh and the display is dark all the time.

What bothers me is that battery voltage is 4V and output from battery chip ic 2.8V (was using a multimeter).

Any help??