The LS4 and its special DoD filters are prone to dry starts. This can cause an audible tap tap tap sound when the motor is cold. It is possible that the Filter under the Oil pressure sending unit is clogged or in need of replacement.

At the same time I am going to address the following codes:

P0520, P0521, P0522, P0523. These codes are related to the Oil Pressure sending unit or switch which means it is in need of replacement. To get this job done you will need the following:

27mm Deep socket with extension and ratchet.

Something that can hook the side of the filter without damaging it if you plan to keep the old filter.

The Old Pressure Switch or Sending unit PN#12616646.

The DoD filter PN#12585328

Clean rags.

Install should take about 10 minutes. Music: http://www.purpleplanet.com