M.T.
When you wash the towels put them thru an extra rinse cycle, sometimes the powder detergent (I use it to) foams up more and especially in towels needs and extra rinse. I never use liquid softner and rarely use dryer sheets on the towels because it can make them less absorbent.
The arm pits of my husbands white under shirts also get yellow and crusty - I spray lemon juice on them when I sort the laundry so it has time to break down everything. Then when I wash I also spray the pits with shout or spray n wash. I find its worse with gel deo/antipers. than solid or spray.
Megan