Ok. It was a coolish day, about 60 degrees high. Went for a drive, came back - parked RX350 and it was in the garage for about 5 hours or so. Opened the garage, and heard a fan/grinding/buzzing sound. It was not LOUD, not dim, just slightly louder then dim. I could hear it from front of RX, a bit more then faintly.

Sounded like it was coming from rear hatch area. Opened hatch, locked it again using push button on inside of hatch door. Sound still there. There is NOTHING in trunk i.e. stuff that could make such a sound.

Started RX350, backed it out of garage, parked it back in garage. Checked - and sound was gone.

FYI - I keep the alarm on at all times. Just force of habit, although not required where we live. Thought maybe alarm malfunction - who knows...

Any ideas/guesses? Puzzled and a bit concerned.

 

It's one of the most technically sophisticated cars you can drive today and it does quite a few things on it's own. Not having the sound to reproduce for us it's guesswork but my guess is it's probably one of the various evaporative gas systems to purge gas's or vapors. They will do this automatically. Drove me nuts at 1st but now I just ignore the odd sounds of a creature still alive

Sometimes it can be in the garage overnight and I'll get in to start it and the key is still in the house. So when I get out to get the key, I hear odd sounds like it was getting ready for me and cancelled the plans. You'll get used to it.

Actually the sound you heard was probably the fuel system purging vapors.

 

yeah my guess would be something to do with the emissions controls.

 

Thanks guys for your quick and reassuring replies.

based on your replies and additional research, I agree - it was probably the fuel system purging vapors. I just never thought about/expected that sound when the RX350 was powered off.

Thats one smart car/SUV.