Yep... sounds like interference to me too (if it's not the magnets).

Make sure you twitch all the high current leads together, and run your RPM sensor wire back to the FADEC as far away as possible from even twitched leads.

I had no end of trouble trying to start my first JJ-3000 until I took Bretts advice and twitched all the high current leads together and re-routed the RPM sensor wire itself. Twitched-together wires make for a neater job as well.

When I added my second JJ-3000 to the test-bench, I made sure all my wires were twitched together from the outset, and it started first pop

BJ