jackdrc:
/usr/bin/jackd -dalsa -r48000 -p128 -n3 -D -Chw:0 -Phw:0,0
The "-P" option is not being fed any argument. Check the
/etc/security/limits.d/99-audio.conf make sure you are in the "audio" group.
Turn off wifi, and rmmod its driver module.
Check /proc/interrupts to make sure the soundcard isn't sharing its IRQ with any other
device in your computer...
I can't think of anything else right now.
By the way, have you tried rebooting your PC? Have you upgraded your kernel?
Good luck!