Ross,

When you make reference to the "oil check valve" is the same part as a Oil Relief Valve in Filter Housing? I also have a similar problem with my 92 400se making a taping noise for a short time upon cold starups. The noise sounds like it's coming from the oil filter housing/distributor cap area (passenger side) of the engine. I'm going to get a Stethoscope from the auto store this weekend and see if I can better isolate the "taping noise" area.

Russell