hmm,

this is one of those things that you are going to have a hard time figuring out. Do you have another heli you could try the BEC in? If so, do that and see if it causes problems there as well. Otherwise, try another bec in your problem heli and see if that fixes it. You could always contact castle and see what they say. After I trashed my last castle bec I bought one from justgofly.com for 12 bucks I think. It has worked great but is pretty finicky on location, I mount it up front right next to the esc.

You could pick one of those up if you don't have a spare and then send the castle in if it turns out to be something wrong.

Why are you running an external bec anyways? were you having power problems?

Is the heli glitching any time the bec/esc/rx are powered up or only when the blades are turning?