Another promo clip on Cartoon Network's Youtube channel, showing a flashback of Bumblebee (talking) with Grimlock and Optimus.
Unfortunately it is geo-blocked, so some screencaps can be seen here.
After getting a VPN, I was able to watch it, and just like Starscream being voicced to try to sound like the Gen1 Starscream, Optimus is voiced to try to imitate Gen1 Optimus.
Also, they annoyingly refer to Teletran as Teletron... like they started to in Beast Wars, before the fans made the writers correct it in-story (Blackarachnia telling others the correct pronunciation).