what makes a pickup microphonic?

[Greenfuz]

???

and can you have a pickup custom wound to be microphonic?

[Mike]

Loose windings.

If the windings aren't tight and are able to move around, the pickup will be microphonic. That is why potting in wax cures a microphonic pickup. The wax fills the tiny little gaps between the coils, and secures them in place.

Once I had a microphonic Tele pickup that was caused by the magnet being poorly secured to the bottom of the pickup.

I imagine you can get a custom loosely-wound pickup, but I doubt it is predictable enough to guarantee a certain microphonic quality.

Mike

[bob the r0bot]

^Nailed it.

Random anecdote: before I changed pickups in my jag, the pickups in it were so microphonic that, when plugged into a high-gain amp, it chorused.

[IEatCats]

Note to self: loosely wind a shitty pickup.

[Achtane]

Note to self: loosely wind a shitty pickup.

Just buy an ancient cheapo nothing pickup off of ebay and carefully heat gun that shit.
BAM, un-potted.

[Greenfuz]

^Nailed it.

Random anecdote: before I changed pickups in my jag, the pickups in it were so microphonic that, when plugged into a high-gain amp, it chorused.

that sounds beautiful