I'm not seeing any complaints about the speaker phone on the Ace 2x but I'm going to my parents place in a little while and I'll try his out and see if I can replicate the issue and come up with a solution. Have you tried turning down the volume to see if the feedback goes away?
I have the Ace 2x as well and I haven't been experiencing any squeal or feedback issues. As Paul mentioned, lowering the volume may help. A long shot, if you wear a hearing aid, it's possible that you may be hearing feedback from the Ace 2x's speaker if the volume level is set to high. Is this happening with both devices?