Also if you hold the guitar with the strings damped and turn up the amp's volume and gain, then with microphonic pickups you'll get a high pitched feedback sound, (the winding lengths on the pickups are small, so the fundamental notes are at a high frequency), a very different sound to normal guitar feedback.

Original PAFs weren't dipped at all, so were all slightly microphonic. The scatterwound nature of the windings kept this to a minimum, as where the wires cross over each other they help to damp any resonance. But sometimes un-potted pickups with neat parallel windings can be very microphonic indeed (especially when it's warm and the windings expand and slacken). I've had to replace three pickups for being very microphonic in the past - so much so that even with a clean amp at a low volume they squealed like mad. These days, I'd probably have a go at potting them myself, though two were only cheap pickups and they got replaced with much better ones.