I've had a similar thing happen with my '86 which has the B230 engine. On two mornings I started the car to back out of the driveway. When I first revved the engine a little, I got a light knock, sort of heavier than a spark knock but lighter than a rod knock. The knock was brief. By the time I backed out and got started down the street, the knock was gone and didn't come back the rest of the day. My car was not used for about a week while I was dong a t-belt and other small repairs. I've not heard that knock since the car went back into use two days ago. My driveway has only a slight slope and the oil level is full. I use synthetic 10-30 oil and have about 220,000 miles on the car. I'll be interested to see what replies you get.