Start by charging the battery back up while you're doing the other search. The chatter noise indicates the starter does not have enough power, so the start solenoid clicks in-out-in-out rapidly.
Did you check your RUN-OFF switch on the handlebars? I once fought with my 750 (or it might have been my 500) when it got bumped to just-barely-OFF once, spent half an hour trying to figure out why it wouldn't start! (This was in 1973, still bugs me...).
If you took the carbs off, you may need to check your fuel line routes, make sure they are not kinked. Make sure fuel flows OK thru the petcock, too. Open the float bowl drain screws and let some fuel fun from the tank thru the whole system, every carb, then close them back up.
Make sure the clamps on the carb hoses are tight, on both ends of every one.