1997 Ford Thunderbird What can this sound mean

Did you replace the spark plugs and wires for maintenance or because of this problem? If the problem wasn't there before you did the wires, that is the most likely suspect. If you mixed up two of them, the problem would have been there right away. When it takes longer to show up, as in a few days to a few weeks, it's often because one of the wires didn't get fully seated on the spark plug. That will cause a small arc at first but enough current will still get though to fire the spark plug, and the engine will run fine. Eventually that arcing burns the metal terminal away in the end of the wire. That arcing always leaves a carbon track behind, and carbon conducts current. The arcing multiplies rapidly to the point you might hear and see arcing alongside the spark plug boot.

I'd start first by inspecting both ends of each spark plug wire. Look way inside the boot, or better yet, try to slide the boots up so you can inspect where the terminals are crimped to the carbon-impregnated string. You're likely to find that string burned away too.

You can also short out one spark plug at a time to see which one causes no change to how the engine idles. That would be the one to inspect first. Use a pick with a small jumper wire between it and the engine block. Slide the pick between the wire and the spark plug boot to ground that spark out.

Don't try to remove a spark plug wire to figure out which cylinder is misfiring. The spark is going to try to jump that gap and will leave a carbon trail behind that promotes more arcing later. Also, the ignition coils in your system fire two spark plugs at the same time. One cylinder is on the compression stroke and one is on the exhaust stroke. That second one is referred to as "waste" spark. When you remove a spark plug wire, both of those spark plugs will stop firing.

You might also find that shorting one spark plug makes the engine run better. That would be a case where the plug you shorted is causing such a bad open circuit that its mate doesn't get enough voltage to fire that spark plug. Shorting the one causing the open circuit returns full voltage, (more than normal voltage) to the other plug, so now you have one shorted plug instead of two misfiring plugs.

I think you're confusing the terminology and that's confusing me. What exactly do you mean by "turning over"? A lot of people think that means the engine starts and runs, but it simply refers to the starter cranking the engine. First it has to crank, (turn over), then it starts and runs. If it's not cranking fast enough for the engine to start, we have to look at that system. If it cranks too long before it starts, that's usually the result of fuel pressure bleeding down when the car sits a while.