Your battery was down with the bad regulator. When you installed the new regulator the alternator load increased substantially to bring the battery back up to where it should be.


The alternator belt slippage because of this is what I believe you are hearing. The best test is there is a small cooling fan in the front of the alternator just behind the pulley.


With the engine off of course if your can turn that fan by hand the belt or belts are far too loose. If ever far away from home and no tools and this occurs.


Get a bar of hand soap and rub it on the v section belt or belts. It will quiet them down and restore their traction until you can get the adjustment done. I believe it is the glycerin component of the soap that aids traction of the belt or belts.