I found one of the weirdest bugs in my life. It seems that powerd's options cause hiss in the audio on my laptop. Here are the options from rc.conf:

powerd_flags="-n min -b min -a adp -r 90 -m 800 -M 2100"


and device.hints:

#turn off connections that don't seem to exist
hint.hdaa.0.nid18.config="conn=None"
hint.hdaa.0.nid26.config="conn=None"
hint.hdaa.0.nid28.config="conn=None"

#speakers
hint.hdaa.0.nid22.config="as=1 seq=0"

#headphones with auto switching
hint.hdaa.0.nid17.config="as=1 seq=15"

#build in microphone
hint.hdaa.0.nid21.config="as=2 seq=0"

#microphone jack with auto switching
hint.hdaa.0.nid20.config="as=2 seq=14"