The servo trying to 'zero' itself out means that its trying to re-center (point straight) or paint wherever your transmitter's stepping is.
Say you turn your transmitter wheel 30 degrees to the right, the xmods have 256 stepping, so we'll assume that your servo turns to its 210 step and your wheel is jammed so that it cannot turn as far as it wants to, say only at its 205th step. The servo will make a buzzing or humming noise as it tries to force that wheel to turn so that the servo ends up at its 210th step.
Its a bit hard to explain, sorry.
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