A little help with balancing the mount to a finer degree than moving the telescope in it's dovetail clamp, is to use a Baader rider clamp and stick some self adhesive car wheel balancing leads to it.
In that way, depending on the amount of weight you stick on it, by sliding the clamp up or down a dovetail plate you can achieve a very nice precise balance.
An other issue, vibrations, is often caused by the way the the mount is attached to the pier.
If the pier has a so called 'rat-cage', the threaded ends between the pier plate and the telescope mounting plate may introduce or boost vibrations, because of the resonance frequency of that construction. The longer the threaded ends are the lower that frequency will be and higher the chance of this phenomenon. The shorter the threaded ends, the higher the resonance frequency will be and the less effect it will have on the PID settings.
Thought I should mention this.