I strongly doubt that you are getting "feedback' through the speaker.
I've never seen a ham transceiver that was designed to output micrphone sidetone from the speaker whether internal or external. Why? Because it serves no purpose, and the only thing that can happen would be actual feedback.
I suspect that you are getting either RF overload from the antenna or common mode RF down the coax.
This question gets asked and answered in several posts every week. It is worth spending some time reviewing the forums. Here are some quick answers.
Procedural point: It is better to post your separate questions rather than piggy back them onto a year old unrelated topic.
-Try reducing power to see if there is a level where problem disappears.
-Clean up your shack, separate cables, coil them out.
-Try putting toroid chokes on your antenna coax, mike cable
-Does problem go away on different bands?
-move antenna further away from shack
-elevate the antenna
-Look at possible ground loops. Do you have ground wires between components? If so try removing them.