Audio Logging Woes

[colmerinoz]

Host Ubuntu 14.04 on Xeon E5-2403 with 24GB RAM
VirtualBox 4.3.14
Headless Guests: MS SBS 2003, Ubuntu 14.04 Samba server, XP Pro SP3 as audio logger 1, Ubuntu 14.04 Server as audio logger 2
Each guests has 1 CPU assigned and 1 to 2 GB RAM.
Managed via phpvirtualbox and/or direct SSH.

Scenario: This is for a community radio station where they are obliged to keep logs of on-air content for a minimum 42 days.

Condition: First two guests OK; running fine and happy.
The two audio loggers run for 24 to 36 hours or so and then lock up, sometimes within an hour of each other, but never actually at the same time.
Both are listening to a shared audio input on the host and recording to wav files. Just after the top of the hour the wave files are closed and converted to mp3 for storage on the Samba server.
The Windows guest is running proprietary logging software called Aircheck. We have had this running for years on a physical XP box.
The Linux logger is using arecord on alsa drivers and converting with lame.
Performance on both is good up until failure. At that point the CPU usage on the host shows more than 100% for each of the failed guests.
After lockup the guests can't be stopped from the phpvirtualbox interface. Only a process kill on the host works. After restarting the guests everything continues well for another day or so.

The Ubuntu logger was the second one built in the hope that it would press on even if the other one failed. This hasn't happened.

I'd be grateful for any fresh ideas on this. I've tried many things with no great change in the problem.