[350HP930]

My 930 with a straight pipe disguised as a muffler where the factory cat and muffler used to be liked to gurgle a lot on deceleration.

After my Andial fuel enrichment device died and I tweaked the mix up using the CIS adjustor screw to fatten the mix up across the board.

The richer idle and decel mix completely got rid of the decel exhaust gurgle.

I take this as a case in point that a 911/930 with reduced back pressure and a correct ~14:1 A/F ratio likes to gurgle on deceleration.

For this reason I assume your options are to live with it or fatten up your idle mixture.