Mystery Squeal

[JCampbell]

I've got this odd noise that's driving me nuts and I was wondering if anyone else has experienced it and maybe even knows where it's coming from.

88 Suburban, tailgate, rear a/c.

It's an odd squeal that comes from the back end somewhere. Varies in volume and length, but the pitch is consistently high. At first, I thought it might have been the squirrel cage rubbing on the blower housing, but I eliminated that. Then I thought it may have been the rear window binding in it's channel, but it doesn't appear to be that either.

It's completely random (at least it seems to be) so replicating it is nearly impossible.

Any thoughts?