How Do I Stop “Junk Mailbox” From Chiming When Opened?

I get a sound notification when I open the Junk Mailbox in Mail on my iPhone 7 iOS 12.1.2.
No other mailbox makes a sound when opened. In Notifications I have chosen Sound “None”.
I haven’t been able to figure out how to stop this.
Thank you for any help you can give.
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Pat R