Random Click - 71 Blazer

[ochre1971]

Just like it the title says, I'm hearing what sounds like a random (seemingly) relay click sound. I happened to notice it the other night while getting a picture of something under the hood for a fellow member. I was in the area of the battery and thought I touched or moved something. Couldn't reproduce it.
Now, at least twice since then I've walked through the garage and heard this same click. One other time as I opened the driver's door to get something...

It sounds like it's coming from behind the AC compressor area, possibly inside the cab in the same area.

All this is obviously while the truck is off.

Anyone have any thoughts as to what this may be? Thanks in advance.

I posted this in the electrical section as well, but thought I may get lucky and find someone over here who has dealt with this before.

BP