Horizontal banding/Stripes - Nifty 50 is acting up.

What would cause horizontal banding like this??
The shot was taken with my XT, and the 50mm f1.8.

There was no filter on the lens, so that is ruled out.

AV mode
1/125th @ f6.3
200 ISO
No flash
The same banding is visible on several vertical shots taken just after this one.

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Was this shot in AI servo? It looks like interference banding to me.

I'm not sure if my wife had it on AI servo at this moment in time or not.

Now that I've read into interference banding, I agree that appears to be what it is.
I'm a bit shocked to see it at 200 ISO since all the things I've read say that it happens at high iso.

Never had this issue with any of my other lenses.

Anyone got a fix? Perhaps lead foil over the focus motor?

I'd send the ole XT into Canon for that one.

Is this something that they can resolve?
Anyone have any feed back on whether or not they can fix it?

If so, what sort of cost is associated with it?