Tough to hear the servo's in those videos...sure the video is low quality, but I think the audio is more important here...
As far as the servo's vibrating/not vibrating... I think when your servo hit there limits (which is where I hear the constant whining) you won't have any vibration because it can't vibrate.
I think what you really have to do is take those servo's off of that 'turret' and figure out where the limits of those servo's really are so you don't confuse a 'no vibration' condition with a servo that's hit it's mechanical (and/or electrical) limit. A pulse width of 1000-2000us for this servo, might not be good for that servo...or it might be just fine.