I just updated to ubuntu 12.04 on my Dell laptop xps 15z.
The trouble is that I hear a slight ticking sound every 3rd second, probably from a fan. This is a new issue in this ubuntu version.
I use the recommended boot options for grub, i.e. acpi_backlight=vendor, but I do not use any acpi=off or acpi=noirq.
Is there a way to fix this issue from ubuntu, by maybe controlling the fans somehow?
EDIT: Notice, the sound goes away as the fan speeds up, (when doing calculations or such), so it is really a fan issue.
EDIT2: I have located the issue: If I use conky 1.9, together with the command execpi for a python application, then the sound appears, and the noise syncs with the update interval for conky (NOT for the update interval for execpi!). The noise seems to be proportional to the complexity of the drawing that is needed. This is very strange, as this issue was not in the prev. version of conky I used.
The solution was to increase the update interval for conky from 0.5 to 3, i.e. update every 3rd second instead of twice a second.