This seems to be a common Janome problem. My machines has done it right from the word go and I should have taken it back but did not only because after some observation I noticed when I have a computer on in the same room it does not like it or when I am sewing on a retreat and other machines are going at the same time. I also have a wireless intercom in my sewing room and that also interfers with it when on.
Solution for me is to not use the foot pedal - only when winding my bobbin and then remove the foot pedal from the machine and use my stop/start button.
Perhaps we should bombard Janome with an email at the sametime complaining about their foot pedals and ask why we are all having this problem. Some computer chip problem or????????? which is common to their machines.