On Monday I wrote about what seemed to me to be unusual knocking after I had my water pump and belts (except timing) changed by my local Volvo dealer. I did not have time to attempt it myself. Anyway. My first drive after the job I noticed what seemed to be excessive knocking. I though perhaps the timing was screwed up or something. I filled my tank up with 93 octane and added the 3/4 quart that was needed to fill the crankcase. The knocking subsided a little but was still there. Responses to my Monday post suggested piston slap and such and that is still possible. Just after my post I did about a 250 mile trip. The car (89 740T)ran fine. Tonight I am sitting in my hotel room after a 110 mile trip. The strangest thing happened on the way here. At about 80 mph which was the average speed I was traveling, I began to hear the knock again. The car seemed to labor and I was suddenly having trouble maintaining 70. I exited and as I reached the end of the ramp, the knocking seemed to stop. So I did a U turn and got back on the interstate and completed my trip without any further problems. WHAT IS GOING ON??? Knock Sensor? Timing? I am totally baffeled! Any sugestions appreciated!