Is it possible for lightning strike to travel up ground / earth pin on a mains outlet?
Put it this way: there is a case on record of ball lightning rolling out of a fireplace, across a room and out the door. Brian Drummond's comment is spot on. The enormous current transients involved, with their associated electric and magnetic fields, can produce completely bizarre effects. For the most part, lightning strike effects can be handled effectively. I suspect that your PC has a good power supply, and there's a spark gap protector in there somewhere. If this is so, then you're seeing and hearing a successful protection incident.

Nonetheless, if this is a common occurrence, I strongly advise that you invest in an external surge/lightning protection unit, and not a cheap one. I well remember, twenty years ago, when I discovered that my phone was dead. After the line was repaired, I discovered that my modem was dead. Opening the case found it full of confetti, which was the innards of several capacitors. The capacitors had not handled the surge produced when lightning hit my phone line very well (which is why my phone line went dead, of course), but the modem did successfully protect my PC.