you have a interesting situation there.
Backfiring into the intake would indicate a vacuum leak
The sound in your video sounds somewhat like a vacuum leak.
But on the other hand your low RPM fuel trims (RKAT) are negative values indicating a rich condition at idle. Vacuum leaks cause lean conditions at idle. Your mid to upper range fuel trims look to be positive values which you would expect under load at mid to upper RPM range. Adding fuel under increased engine load.
Porsche and or Durametric expresses fuel trims in a manner that I am not very familiar with so I could be off on what I think I see.
What are your pre cat o2 sensors doing at idle and again at say 3000 RPM???
If fuel trims are going negative at low RPM I would expect the O2 sensors to be showing a rich condition. Voltage above .500 mil volts then dropping as RPM increases and fuel trims go positive.
The sound in your video also (to me) sounds a little like a possible exhaust restriction.
Any chance the Cats are plugging up??
Don't know if I have helped or added confusion
But those are my thoughts
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