FreeBSD 5 NFS server random freezes

[Guy Van Sanden]

Hello

I have FreeBSD 5.0 running on my home-server.
It servers NIS, NFS, NTP, CUPS, HTTP, MySQL, ...
The clients are mostly Linux (Mandrake 9.0 and 9.1).

Every once in a while, the NFS server just seems to freeze.
The machine is running, I can ping and ssh in and it still serves NIS
and
all other functions.
But NFS is just plain dead.  Killing mountd and restarting it doesn't
help.
If I do ls /net/{machinename} it says: "Resource temporary unavailable".

At that point, I have two solutions, either reboot the machine, or drop
to
single-user mode first, and multi-user then.

I can't find anything in the logs, nor can I find a link between some
action
and the crash.  I happens during heavy loads, it happens on light loads.
There's only one thing in the logs I can't explain, but I can't find the
relation:
--
Apr 22 13:39:51 nemesis kernel: stray irq 7
Apr 22 13:40:16 nemesis last message repeated 4 times
Apr 22 13:40:16 nemesis kernel: got 5 stray irq 7's: not logging anymore
--

Is anyone experiencing this?
Any thoughts?

Kind regards

Guy