Thank you for reaching out to the Samsung community! We would like to inform you that it is the default feature of the device as device will vibrate when you launch Google assistant and Bixby by voice.
Be sure to hit ♡ when you find an answer that works for you. For Further assistance, you can get in touch with us via Live Chat option by following- http://livechat.support.samsung.com/Customer_new/IN. You can also connect us via Samsung Members web community by following mentioned url-https://community.samsungmembers.com/en_IN#/