how can is top my sparkplugs arcing?

[Dead Eye]

its hard to tell really as the exhaust is quite loud. if that was the case what options would i have to fix it?

Hard to say without some further testing. Have you tried swapping the spark plugs around? How old are the plugs / when did you replace them?

If it is a leak then it probably means bad threads on either the spark plug (fingers crossed) or in the head. If the former, then a new plug should stop it, if the latter then it means either new head or having it helicoiled. As for the cause - previous owner / mechanic could have tightened the spark plug too much and stripped the threads?

All of this is complete guess work at this stage as its all based on an assumption.

First step, swap the plug with a different cylinder and test - if you can, stick a photo up of the plug #3