When sharpening western wood chisels over 1 ½" wide, vibration seems to occur at the grinding wheel. From reading related topics, it appears that this may be overcome by moving the chisel more rapidly from side to side. If the wheel has been trued, is there any other cause for this vibration?
Is the vibration accompanied by a loud chatter? This happens, it's just a condition known as resonance. Change the amount of force you're applying to the tool, or just remove the tool from the wheel and make contact again. This usually happens to me when the tool is very close to being sharpened, or has already been sharpened to the point that additional contact with the wheel won't make it any sharper.
Sounds similar to your description, so I'll have another go at it, alter the applied force ,get a feel for what's happening, and then get back to you. Thanx