i don't think that is normal (but neither am i). did you check the mounting screws to make sure they are tight? maybe someone with more marlin experience can help more but i would check all screws first.
The barrel band out near the front sight has a screw in it. The screw feeds from right to left. In the mag tube, under that barrel band, is a slot for the screw to go through and a slight groove under the barrel. Like Oleroy said, I would check there first. If the two slots are aligned and the screw is through there, the mag tube has very little, if any, wiggle room.
Also, the end cap at the end of the forearm (or band around the forearm) needs to be tight. When the forearm is snugged up well into the receiver, and the end cap is in the right place, there is tension placed on the mag tube....upward tension - toward the barrel. Check that the forearm is snugged against the receiver and that the screw is tight (or rather...snug).
Does it work allright otherwise? Feeding rounds when levered?
What if you removed the screw from the band near the front sight? Just push the band gently towards the rear of rifle - away from the front sight. Then you can see if the grooves I was speaking about are lined up. Also check the screw....maybe there's too much gap between the barrel and the mag tube and the screw is not keeping the grooves aligned. That might lead back to the forearm band and the fit at the receiver.
Maybe some more knowledgeable guys will chime in, but I'm thinking the problem is there at the front band.
Found a similar problem and the barrel band was upside down taking it off and flipping it top to bottom it solved the problem. Tolerances can be part of the problem (sorry I don't remember which Marlin it was).