NoteBoat seems to have nailed the likely possibilities:
There's a chance they have doubts about the new guitarist. Bring your gear, but leave it in the car. That way you're covered under any of the three scenarios that are most likely:
1. the bass player wants some feedback about the band, and after the rehearsal you'll have a beer or two and he'll get your opinion
2. he's curious about your progress and wants to jam a bit after the rehearsal
3. they're thinking a member might have to go, and you'll audition after the rehearsal is over.
The elephant in the room though seems to be that you wouldn't be able to accept an invitation to join a regular band even if they were interested and some sort of audition thing happened. As you said:
rparker wrote:It will be murder on my head, even with good ear plugs. I will pay a hefty price for this. I only do something this stupid once every few months. It's more for my sanity than anything else. One night of major-league Migraine is a small price to pay for sanity. I would not want to do something like this 2-3 times a week, but once in a while, just to feel normal, it's all worth it.
In your position I'd be very happy to keep a pleasant fantasy going that they might want me to join the band - or at least see me as a worthy candidate - but I'd still know that it wasn't going to happen. So it would come down to whether I might get asked to jam along or not. Given that you'll be dropped off by your wife, keeping a guitar and amp out of sight isn't an option. There's no way I'd turn up with a bunch of gear unless I had a clearer signal about what he had in mind.
If I was running a band practice, no matter how unstructured, I doubt that I'd want to unbalance things by adding an untried player on a one-off basis. But I might well be happy to have a jam with an old buddy later. So maybe that's a possible angle to take? Email and tell him you're looking forward to listening in on their practice and ask if he's expecting you to bring a guitar along for a jam afterwards
? If he does have any ideas about having you participate in any way then he'll surely say something, and nobody is going to lose face or get embarrassed about saying no at the time, or disappointed if things don't pan out as imagined (on either side).
Either way, enjoy yourself Roy, you deserve some fun times out.