@Bob Mosa,
OK. Well, if you perceive a change in her, but she says there is no change ... is there a change in you?
There is a reality here that you have some, all be it presently slight, distrust of your wife ... Maybe after a couple of years of marriage your wife feels totally safe in her own skin because of you and your support ... and as such can come 'out of her shell'.
My wife is nearly 9 years my junior. When we met she had be doing professional modelling, so she is a tall, pretty lady. She is also extremely intelligent and has gone on to become a Dr of Psychology and of Criminology.
It is my presence in her life for the past 30 years which allowed to her to fully explore her sexuality; because I keep her safe, grounded and instilled confidence in her. Maybe your wife is in the same place with yourself?
In all honesty you need to communicate more with her .... Be specific, do not hint at anything ... Say 'Strange guys, topless; concerned and uncomfortable' and see what happens.
What I do know is if a couple face the world together as one, then no harm will befall their relationship 99.999% of the time ... So you have to keep asking her until you get an answer you at least understand, is sensible and it adequately covers what you feel.
If you want any more advice, pm me. Cheers and good fortune to you both.