I have an occasional clicking/tapping sound that seems to be coming from my valves on my '97 850. If the engine idles at length it will start. If i drive at reasonable highway speeds at length it will also start. For a month after I change the oil it doesn't seem to be as much of an issue. Is this an issue with my oil pressure, or possibly delivery of oil to my valves?

 

I think the owners manual mentions clicking from the valves. It may be the fuel you are using.

Do you have a CEL light? Is your car turbo? How many miles? How long have you owned it? How long has the clicking noise being going on since you've owned it?