Had the same/similar problem with mine, drove me mad for weeks.
Turned out that some of the electrical connectors had a small build up of corrosion/rust which resulted in the connectors not sitting together properly, hence the slight dimming & flashing. :embarassed:
...all i did was use a little sandpaper to rub away any build up of corrosion, just until the connector became shiny again, a quick spray of WD40, reconnected & tightened them up. been Ok ever since.
Thinking about it now... it may just be the earthing cable that needs checking.
Hope this helps you out.
(PS. i found it used to play-up more when the weather was cold & damp)
