That is pretty uncharacteristic of Magnus heads, but if it is truly the head, send them back and they'll replace them pronto. I am fairly certain that Magnus spin tests their heads before they go out the door, but I could be confusing them with another brand that does that.

Before I did any of that though, I would spin the shaft without the head and make sure it spins completely true. Anything that makes the arrow itself not spin true without a BH on it will seem like a very, very small wobble in the shaft. Then it is more pronounced when the broadhead is attached and is easier to see; that is, if it is not the broadhead. The other thing I would try that has made an enormous difference in how my arrows are balanced and spin is using a G5 ASD on the inserts to square the faces up. Even if there is a slight inperfection in the way the ferul meets up with the face of the insert, you will get a wobble. The ASD is one of the best arrow tools to come down the pike in a long, long time.