Not sure if this adds any value to your problem or not. Many years ago I had a E36 M3 and at idle it made a ticking noise that came from the valve cover. Turned out to be O rings for the lifter or the seals and it was allowing the oil to drain back down to quickly. If you just raised the rpms a little the noise went away because you were throwing more oil up top. Seal or o rings were replaced and noise went away. The pats were about 100.00 but the labor was around 1000.00 and this was at an INDy shop. Dealer would have been a lot more!