Microphonic pickups on multiple guitars - what gives?

[mattack]

I have two electric guitars, a 1983 Gibson SG, and a 2001 Gibson Les Paul... I bought the SG used in late 2001, it still has the same pickups in it as when I bought it - I have no idea if they're original or not. The LP also bought used, in 2012, and I immediately put new DiMarzio pups in it.

Two weeks ago I noticed the SG was a extra squeally, and sure enough, the bridge pickup is microphonic (I didn't test the neck). Last night, between songs at band practice, I tapped the LP with my pick and heard it through the amp. Tested both bridge and neck pickups, and they're both microphonic. What the heck?

What are the odds that 4 year old pickups, and at least 15 year old pickups would go microphonic within the same two-week period? What could I be doing to facilitate that? Could it be the weather? Philly summers are hot and humid, this one especially so.

And does repotting them generally help?

[Chankgeez]

Is it a tube amp? If so, are you sure one of the tubes isn't microphonic?

[ALLisNOISE]

Have you left them in a hot car or practice space recently?
The wax can melt, causing the pickups to go microphonic.
If you pull the pickups and there's a waxy substance in the cavity, then that's most likely what happened.
I can't speak for repotting, but I assume it would work if done in a professional manner.

[rustywire]

I've had cables-going-bad turn out to be the culprit, displaying similar symptoms

[mattack]

Is it a tube amp? If so, are you sure one of the tubes isn't microphonic?

Two guitars, two different amps... both tube amps. One amp fresh out of the shop, so the tubes are likely not the culprit there. The other, I can talk into the pickup and it comes out the amp. I don't think that's the tubes either.

Have you left them in a hot car or practice space recently?
The wax can melt, causing the pickups to go microphonic.
If you pull the pickups and there's a waxy substance in the cavity, then that's most likely what happened.
I can't speak for repotting, but I assume it would work if done in a professional manner.

I don't leave my guitar in a the car for longer than it takes to get where I'm going (practice or a show). My house has central air, both practice spaces are in basements, but I don't leave my guitars there... I'll look for wax residue in the pickup cavities. Thanks.

I've had cables-going-bad turn out to be the culprit, displaying similar symptoms

My cables are the one constant between the guitars and amps, though one cable is only a few months old. I'll try different cables.