What year is your ML?
Is it a 320 or a 430?

We had problems with the rockers making a racking noise and replaced tons of them under warranty?

I am familiar with the engine tick noise going away after warm up or a fresh oil change, but if a fresh Mobil-1 oil change does not do it, you may want to look into getting the rockers replaced.

It is a very simple job that requires removal of the valve cover and removal of the rocker shafts and placing the rockers on a special jig that holds them in place while you take a steel rod and push the old rockers off the rocker shaft and put the new ones on one at a time.
Then you put the shafts back on, torque the bolts, put a new v/c gasket on and you're D.U.N - done!

It's actually a fun job to do if you got all the special tools of course.

Usually the noise would come from the drivers side only, in most cases and we replaced quite a few sets of them at the dealer.