BMW Repair: BMW - engine knock, heartbeat sound, bmw engine

Question
Have a 1998 328I VIN:AV58600.  Had a cracked cylinder head that has been repaired (some water did make it through the engine)and oil was replaced.  After a couple of follow up visits to deal with a clicking sound that matched the speed of the engine (can't recall exactly what the mechanic called it but it involved something getting pressurized), I have a car that runs quiet while looking under the hood.  A noise that occurred prior to the head being replaced is still present following all the work done.  It's a single "heartbeat" sound that can only be heard inside the car while idling.  It's somewhat rhythmic and occasionally a two beat occurs.  With the hood down (can't be heard looking under the hood directly) leaning all over and under the car, the sounds seems to be coming from behind the dash board center to passenger side of vehicle.  With a gentle increase in RPMs, the noise does not accelerate.  A/C on or off it's present but has come and gone with the A/C on being turned off.  Any thoughts?

Answer
Richard the A/C expansion valves have been known to make some odd noises. Other than that is is near impossible to diagnose noises over the internet. See if you can narrow down under what conditions it happens exactly. And get your head under the dash to pin point the noise.
-Evan