Had this 99 sc300 (85k miles) for 2 months and this only happened once:

Parked car at night, woke up in the morning and heard a really fast clicking, buzzing type noise from under the hood. Couldnt open doors with remote and couldnt start car, battery was really low, almost dead.
-After I popped hood I heard the noise was coming from the fuse box area, maybe a relay or something. Unfortunately I disconnected the battery before I could see what it specifically was was and now I cant recreate the problem...I just dont want to get stranded so I want to fix the issue before it happens again.

Any ideas?

 

There is ZERO chance of anyone being able to tell you what that is without it being examined. The only thing I can tell you for heavy drain like that is that the regulator in the alternator can short and drain the battery while parked.

 

well my intention was to find out if there was a common issue...for example on some other lexuses, they have a similar issue with similar symptoms and the cause is a short in the ignition switch more often than not. Wanted to see if the SC has a similar problem.

Interesting you mention the voltage regulator BECAUSE, the autozone diagnostic machine (hooks up to battery while car is started and run) said my voltage regulator is bad. But when I hooked up a multimeter to my battery while running it was a steady 13.7v at idle when hot. Does that help?

 

There is nothing common about electrical drain. Everything in the car is a suspect in the crime. If you've been told twice the regulator is bad then..................

 

Ok so no known issues with the sc's ignition switch huh? Im positive the buzzing noise was from the fuse box, so could the voltage regulator even be related to that even if it was shorting?