The K&N part number is 33-3051
The "sound deadening foam" is a piece of foam in the bottom of the stock airbox, that's held in place with 3 push in plastic retainers. I assumed it was there to deaden the intake sound.
I removed it when I installed my K&N filter, hoping that would increase sound and maybe airflow. I think my intake sounds better now, but I could be imagining it.
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My 2017 M240i: MHD, xHP, Modded OE Intake, AA GESi 400 CPSI Cat DP, Dinan Mid-pipe, M Performance LSD & Rear Diffuser, BMS Exhaust Tips, Apex EC-7 Wheels, M-Tech Front Lip, iND Painted Mirror Caps, Smoked Reflectors