Turns out that, over time, build-up of detergent and fabric softeners can cause towels to lose their absorbency, making them take longer to dry. Ironically, the thing I was doing to make my towels smell good, washing them with fabric softener, was causing them to smell funky. Ugh.
Not to worry, though, it's a super easy fix. All you need is hot water, vinegar, and baking soda. A washing machine is a big time saver, but is not necessary.
First, wash the towels in hot water, with no detergent, adding 1-2 c. (depending on the size of your load) of vinegar to the rinse water. Then, wash the towels again in hot water, adding 1/2-1 c. of baking soda (make sure it dissolves) to the rinse. Dry the towels completely.
That's it! Funky odors are banished.
Our bath rugs were also smelling a little funky, so I used this technique with them as well. Worked like a charm.
So, um, if you've experienced funky towels, could you please leave a comment to let me know I'm not alone in this? Feel free to use a fake name...