I have a 3" diameter hole in my bell housing of the transmission I don't know

All you need to do is clean area and use some Permatex clear RTV silicone ADHESIVE to glue a sheet metal patch on it then duct tape it and let it set for 12 hrs. I wouldn't drill holes and use screws unless you are sure it won't interfere with torque converter or drill into something you can't repair! Clean is the key word! Use carb. or brake cleaner, let it dry then install patch. This adhesive is the best thing you can use, tried and true!

Do you also notice a rattling sound when you drive 50 mph?

JB WELD fixes a lot of damage! My brother patched a hole in an old 6 cylinder truck engine, on the water jacket, and it stayed fixed for years!