[ben]

I seem to remember this problem.
First thing to do is check the back tension is in spec.
Next, set up the roller guides on the drum.
Then, then look at the AC head adjustment and centre the tracking.

Note that if the drum has been replaced at some point and not seated correctly this band of noise will be impossible to remove (I had this once on a VCR whose chassis was bent! Also heard of one case where there was a splash of solder under the drum which cocked up the angle). This would, fortunately, not seem to be the case here, as you say you can adjust the noise out by moving the control.

You will ideally need test gear and alignment tapes to get this done accurately.