I had my battery tested the other day, it registered as being good. But I
noticed the positive terminal and post was quite corroded.
I removed the terminal, mixed water and baking soda and poured it on the posts
and the battery to neutralize the buildup. I then cleaned the post and terminal
and battery, and put everything back together.
Now I have ignition noise in am radio. Will this go away when I drive a few
miles and the computer comes up to speed again?

What could have caused this? Cleaning the battery was the ONLY THING I DID.