As I worked through my "new" '93 940 NA, Regina, 100K miles, I finally got around to replacing the original spark wires. They definitely need to be replaced. One had a split boot at the plug, and two had intermittant bad connections inside the boot. The wires worked but any bad connections inside the wires might cause a high voltage condition at the coil with possible damage to the coil. The originals were Bougi and that's what I replaced them with.

Your pinging sound has become a real challenge! If your timing is set right and you are using premium, you shouldn't have pinging. The possibility of excessive carbon deposits comes to mind. There are ways of cleaning these out but I've never had to do it. Have you checked the timing with a timing light? Does the timing advance normally as you increase the RPM?

I have had a rattling sound from under the hood on a couple of cars years ago, not Volvos. I'm not sure I remember exactly but I think one case was the power steering pump bearing wearing out, the othe may have been the water pump bearing. Also do the t-belt tensioner adjustment, takes a couple of minutes to do.