the other day, I went out for a quick highway drive, and when I pulled in to turn around, I thought a plug wire had come off (sounded like the spark arcing off something under the hood). I checked, and all the wires were on and firing, but it was tapping like crazy. Was going to pull the valve covers off and check everything out, but I decided to check (and re-tighten) the exhaust manifold bolts instead.