The vacuum switchover assembly is on the passenger side of the console. This noise is coming directly from the CCU itself.

It is definately coming from a loose something. When it starts you can tap on the dash and make it click, bumps in the road, etc.

But it doesn't do it at first. Seems like when it gets to that intermediate stage where it begins switching to maintain temp is when it happens.

What's got me so confused, if it was electrical then why does it continue even with the CCU off? Where's the power coming from?

Could it be in the Temp Control Unit below the glove compartment?