[CentOS] centos 6.5 input lag

I have a CentOS 6.5 x86_64 system that's been running problem-free for
quite a while.

Recently, it's locked-up hard several times.  It's a headless server,
but I do have IP KVM.  However, when it's locked up, all I can see are
a few lines of kernel stack trace.  No hints to the problem in the
system logs.  I even enabled remote logging of syslog, hoping to catch
the errors that way.  No luck.

I ran memtest86+ for about 36 errors, no problems.

I've tried to strip away just about all running services.  It's just a
home file server.  I haven't had a crash in a while, but I also
haven't had it running very long.

But even while it's up, I have severe input lag in the shell.  I'll
type a few characters, and two to 10 or so seconds pass before
anything echoes to the screen.

I've checked top, practically zero CPU load.

It's not swapping - 16 GB of RAM, 0 swap used.  Most memory heavy
process is java (for CrashPlan backups).

iostat shows 0% disk utilization.

Anyone seen anything like this?  Where else can I check to try to
determine the source of this lag (which I suspect might be related to
the recent crashes)?

Thanks,
Matt