It varies not just by brand or model. Even from unit to unit. Some are worse than others. I think it's the bearings in the shaft in some instances. Out of 4 bcz2401s trimmers, 2 were very smooth, one had mild vibes, one was almost unusable. If you remove the power head, and swap it to the trimmer head end of the shaft, often the vibe just goes away, or is greatly diminished. You may need to drill a hole in the aluminum shaft for the set screw. Be careful with the set screw in the casting. The casting is pretty thin.