[AndyM1978]

Could be a loose sparkplug that is allowing gasses to escape, which could force the plug wire off. The part of the plug wire that attaches to the plug is designed to provide an airtight seal inside the hole it slides down. When I pull my plug wires off, I get this noticable suction noise along with some resistance until it "pops" all the way out. I've never heard of anyone having this problem, but I'm sure it would be possible.