Intermittent beeping noise from speaker

[sharptooth]

I've installed Mint 14 (Cinnamon) onto an old Sony Vaio laptop and am having an issue with the sound card. During boot and once logged in, a random double beep noise emits from the left internal speaker. The noise doesn't seem to be linked to hard disk or network activity and I suspect that the problem may lie with the soundcard's input. When I open the Sound settings and select the Input tab, what I usually (but not always) see is the Connector drop down options rapidly switching between Line In and Microphone. Attempting to manually select one of these options fails to achieve anything. I have turned the input volume of both input types Off but this still doesn't seem to have fixed the issue.
I tried the first suggestion made here http://forums.linuxmint.com/viewtopic.php?f=90&t=111805 however this did not seem to do anything at all. I also read another post suggesting an issue with the internal wireless adapter, but I have no evidence to support this being the issue.
Does anyone have any ideas or suggestions as to how to either fix or further diagnose this issue?
Thanks in advance...