Comment 50 for bug 1087519

Both you and me we do have new mobos. Yours is decent Intel piece, mine decent AMD one. One clue more to look for problem source on operating system's side.

 Dont worry about system boot upon GRUB_CMDLINE_LINUX... change. You can always play with kernel options at boot time and revert changes.

"8250.nr_uarts=5" is used by me to limit unnecessary memory occupation by inexsisting ports. Standard 3.x.x kernel reserves room for 32 uarts, often invain.
You can limit the number by this option or leave 32 as it is.

I see IRQ 17 is shared between modem and sound card. Try to switch off audio in BIOS or pull out of the slot if it is a card.

What I found most interesting is that IRQ 17 appears in /proc/interrupts only while using minicom. It should be there or missing all the time, AFAIK

Kernel complains about "nobody cares IRQ 17" shall be displayed on every console, even prior to any login action. This is a critical system message and as such is broadcasted ( as ordered by syslog.conf ).