Well, it seems that the little crunching, rattling, pinging noise that I was certain was not pinging, seems in fact to be pinging. It's weird. It only appears under the LIGHTEST of acceleration and when you LIGHTLY let off of the accelerator. It does not ping under even moderate load or acceleration, or under even heavier load or acceleration. I never drive the car HARD, so I don't know about this condition. I wonder about a couple of things on this '94 945T with only 88K miles, two previous owners, full documentation of all service history, Mobil 1 10W-30 routinely, premium fuel at all times, new plugs (Bosch Plats), PO says this ever so slight (but VERY annoying) ping has been present for him since his purchase of car at 20K:

1) Is this possibly related to a vacuum leak of some kind?
2) Is the knock sensor not working (despite the PO's invoice from Volvo service which says that in last 18K miles, knock sensor checked out ok)?
3) Is the car timed incorrectly?
4) Could this be more of a crank or cam bearing situation rather than pre-ignition given the predictable times it happens. (Note: it will even "ping" under MILD acceleration from a standstill? It never "pings" under any kind of load or sound acceleration.

The way I detected this being more of a ping than anything else, was to sit in the driver's seat, open door, in neutral, holding the door chime switch, lightly put pressure on the accelerator but in quick bursts and it will sometimes appear.

This appears to have been a long standing problem as I noticed it when i test drove the vehicle. The PO stated that this mild pinging has been there since he and his wife took the car at approx 20K miles. They reported it as per customer complaints on the work orders, but apparently Volvo mechanics either did not hear it, or were not concerned with it, or just simply glossed over this. It's still there, but really detracts from the pleasure of driving the car, which I am currently trying to develop some rapport with. I've driven this car less than 100 miles since i bought it, leaving it parked and only driving it when it's time to get dressed up. It's a GORGEOUS car, and I have other cars for daily drivers, but I'd sure like to resolve this pinging problem and actually put some miles on a car which I believe should probably be driven much more. Thnks to all for the wealth of information, and collective wisdom of this board. Had it not been for the support of enthusiasts on this board, I'd of never purchased a Volvo and kept driving Toyotas. Thanks again.

Sincerely,

JB