That noise is the sound of compressed air escaping. Hopefully it is just the spark plug, the worst thing is a burned valve. Some of the debris may have got caught in the valve seat.
The valve clearance check you are going to do should find if there is debris on the seat - it should show up as a large clearance on that valve.
If the valve is burnt and has a hole, it may show up as zero clearance - and that is a lot more work involving the timing belt - something I haven't tackled yet.
This is one reason why I don't believe the torque value that the plug manufacturers use on the spark plugs - specially when they are new. I say crush that gasket flat so the plug is tight and won't loosen up and come out - which is no doubt what happened to the original plug.
Of course you don't want to overtighten the plug, but if you put new plugs in, go back after a couple of 100 miles and re-tigten the plugs. I also use chain spray (from my motorbikes) on the threads, so I can get them out next time. Dry is bad.
The valve clearance check you are going to do should find if there is debris on the seat - it should show up as a large clearance on that valve.
If the valve is burnt and has a hole, it may show up as zero clearance - and that is a lot more work involving the timing belt - something I haven't tackled yet.
This is one reason why I don't believe the torque value that the plug manufacturers use on the spark plugs - specially when they are new. I say crush that gasket flat so the plug is tight and won't loosen up and come out - which is no doubt what happened to the original plug.
Of course you don't want to overtighten the plug, but if you put new plugs in, go back after a couple of 100 miles and re-tigten the plugs. I also use chain spray (from my motorbikes) on the threads, so I can get them out next time. Dry is bad.