Siri —- uh huh

There is no way to make it stop that I am aware of. I've heard if you hesitate when you ask Siri a question, you will get that type of reply. You can provide feedback to Apple that you are not in favor of that type of response here, Feedback - iPhone - Apple

Hello ~ When asking Siri something …Hey Siri what time is it? Don’t pause between Hey Siri and your question. It eliminates the “uh huhhh”

~Katana-San~

Go to Settings  > Siri & Search, then do any of the following:

• Change the voice for Siri: (not available in all languages) Tap Siri Voice, then choose a different variety or voice.
• Change when Siri provides voice responses: Tap Siri Responses, then choose an option below Spoken Responses.
• Always see the response from Siri onscreen: Tap Siri Responses, then turn on Always Show Siri Captions.
• See your request onscreen: Tap Siri Responses, then turn on Always Show Speech.

Found this:

https://www.youtube.com/watch?v=ev7JLVsjSas

Hope this assists.

Also, what iOS are you using? I am up to date and have never heard her respond via “Uh huh”