For an unrelated reason I just checked the console on my Mac and found that an executable was being called every few mins, that did not exist. WTF!
I used to have a 3G modem made by Huawei (T-Mobile). The software dialler was pretty rubbish, and it appears that the naffness continued after I removed it. It had placed a file in my Launchpad folder which supposedly checked whether there was an updated version of the software available (note: in 18 months of running this software there never was!).
Anyway the upshot of it that it’s not just the StartupItems Preference Pane that shows such items. Also check the following folders: