Re: Mud Wren...
Carolina Wrens are notorious for building nests in places such as under roofs, in baskets, etc. Carolina Wrens are quite similar to House Wrens, except they have a stronger white eyeline and buffier underparts. Carolina Wren is also the more likely of the two to be nesting in SE Oklahoma - the southern edge of the House Wren's summer range is in the upper half of Oklahoma.
The other option would be a Bewick's Wren - like the Carolina except darker overall - but Bewick's is less common and doesn't usually nest around man-made structures. I'd go with Carolina Wren
TX Century Club Counties: 34
Collin Co. 252 (Barn Owl) - 230 in 2013