If the TV is announcing "volume" changes, then I think you may have a similar feature on your TV that you need to disable. The Roku accessibility will only announce selections since Roku devices do not have volume controls/features.
I think it is your TV talking to you, not the Roku.
Post back the model of your TV if you need more help and maybe can look for some info on it.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102