Report it to Brumbek in the AN thread, with the name of the interior cell and preferably a screenshot of the problem, and I'd imagine he'd take a look at it. It's basically because the vanilla meshes are rubbish and have holes in them everywhere, IIRC.
It happens pretty much all over the place, so I'm not sure what he could do about it. But then again, considering the work he's put in so far I shouldn't underestimate him

As noted below, I'm not sure it's mod related or even mod-fixable anymore. But unless someone comes up with something clever, I guess I'll take a few snaps and post them.
Aye, I've suffered through this anomaly since re-installing Oblivion several months ago, as documented in http://www.gamesas.com/index.php?/topic/1107968-sunglare-error. It's exacerbated for me by using Beaming Sunglare. One other person reported being afflicted. Note that I DO NOT use either AN or Immersive Interiors.
Like you, I've been putting up with it, since it causes no stability or FPS issues, and is only evident at certain times of day. But as you say, in certain situations it can be very annoying.
No one has as yet offered a cause or cure. I know I should strip my installation of all mods and do exhaustive tests to find the culprit, but it just hasn't seem worth the effort. (That said, I did do some experimentation, but it unearthed nothing.) In any case, I'm not 100% convinced the issue is mod related, since my mod list is quite similar now to what it was during my first play-through, and I didn't have the issue back then. Still, SOMETHING has to be causing it.
-Decrepit-
Sorry to hear you're suffering from the same problem, but also glad I'm not the only one

.
Been searching all over the net for this, but the only cases I've found are you and the user 'sauron0000' on the TESNexus comment-section of that Beaming Sunglare mod.
We seem to have 1 thing in common though...
You have a GTX470.
'sauron0000' has a GTX460.
And I have a GTX480.
Could it realy be a card/driver issue? Could explain ther "rarity" of the problem though.
I'm currently running Windows 7, 258.95 drivers with forced v-sync, triple buffering and 1 maximum pre-rendered frame. As much as I hate v-sync, because it gives me mouse-lag, my fps hits 1.5k in menus and containers. That causes my card to make a high pitched screaming noise which is very unnerving. Only way to stop it is locking fps through v-sync (tried mods, they lock ingame and unlocks in menus). You don't happen to have this problem aswell?

Guess I should try fiddeling abit with control panel settings, never know what might help.