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Welcome to the Club, Graham. You will enjoy your Jaguar. I don't get oily hands any more, but it does not seem like a difficult fix. Regards, Peter.

That, to me, sounds like fuel igniting in the inlet. In the old days of carburettors, you could get this. It was know as 'spit-back' then, and fuel would be 'spat' back into the carburettor and ignited. Removing the top mounted air filters could sometimes result in flames being spat into your face as it ignited. In those days it was caused by incorrect timing. Given that your Jag will be electronically controlled, timing is not adjustable. However, you say the car runs fine, which I'm sure it does, above idle speed. At idle, the flywheel smooths out any imperfections due to its mass which turns the crank via momentum. Any minor misfires will be largely unfelt due to the flywheel mass, but will still result in a lack of pressure on any given piston. If there is any incorrect burning of fuel in the chamber, it will be forced into the next available opening, usually the exhaust and burn up there. There are various things which can cause fuel ignition in the inlet, the main one being a worn inlet valve, but that would result in a rhythmic sound as the same piston would have the fault every time. Generally, sounds like this are caused by poor ignition - ie spark plugs & leads. What happens is that the voltage applied to the ignition High-Tension (HT) side increases with rpm (to a point), so at idle the spark is weaker than at higher revs, purely because it doesn't need to be. At this lower voltage (bear in mind that it is still around 12000 volts!), it travels all the way from the coil, through the HT lead and down the spark plug where it jumps across the gap to earth, causing the spark which ignites the fuel/air mixture. As the revs increase, so does the voltage produced in the coils, and any insulation weaknesses cause the current to leak to earth before reaching the spark plug gap, which results in either a misfire, or a poor ignition which means the fuel in the chamber doesn't ignite fully and you get unburnt fuel left over. At low engine speeds, ie- idle speed, the flywheel momentum is enough to disguise these minor misfires and you generally won't feel them, but the lack of a full spark causes the misfire nonetheless. At higher speeds (and it only needs 100-200rpm extra) the flywheel has more momentum and masks them perfectly, and the coils are producing more voltage which reults in a bigger spark and the missfire is largely unnoticed unless its quite large. The engine in the video link you posted is seriously misfiring whilst the guy is trying to rev it up. The issue here is that these misfires cause damage. If it's popping like that in the inlet (and I'm diagnosing over the internet here), then it's as a result of fuel being ignited in places where it shouldn't be. It's possible, with EGR circuits these days, that it is igniting in the exhaust and being heard throughout the system, but if it is a misfire causing it, to that degree, I'd be concerned. If it's left it will cause grooves to be etched into the valve seats and that requires the fault rectifying in the first place and then the valves regrinding or the seats and valves replacing. Cylinder head off and not cheap. On a dark night away from street lights, crack open the bonnet and have someone rev the engine from idle quite briskly. If you have any problems with HT lead insulation, you'll see them light up like a chritmas tree as the current leaks to earth along them. Keep your fingers off them. I know from experience what 25000 volts feels like! If they are good, check each spark plug. If they are old, replace them. Signs of leakage are grey lines running along them. It looks like someone has drawn a line down them with an HB pencil. This is where the current is 'tracking' to earth instead of flowing through the centre. If it's not caused by ignition, then there really are only a couple of alternatives. Faulty head gasket or worn valves. If the gasket has blown between two adjacent cylinders, the gasses will be ignited in one, then forced through the gap into the adjacent one. That adjacent one will have a valve open as it will be on a different part of the 4-stroke cycle, and the burning gasses will enter the inlet or exhaust as a result. Again, I'd expect a rhythmic mis-fire if that were the case, hence why I suspect ignition faults with your engine as the insulation on 6 HT leads will break down pretty much simultaneously and cause random misfiring instead