Mine was the stock air box. It was vibrating like crazy. I put on a typhoon intake and it went away.

 

if you have fog lights, i would check those

 

I have go the part that makes this noise under load in drive and then goes away. It is the compressor on the A/C unit. I have had mine replace twice now for this problem. Now the dealer is trying to tell me that this is a "characteristic" of the system. I am now beginning the arbitration with them over this.

I also have had pin pointed another noise…it is a high-pitched whine…it happens at around 2800-3200rpms in OD. The dealer just last night determined that it was the tranny. They were ready to replace it until they found out I had began arbitration.

PLEASE check these two items out on you 05 xb auto. The more we report these type of items, the more Scion will likely agree that they got issues.

 

Whoa, peeps! Most respondents so far take no note of the KEY symptom that I've bolded in the quote above.

The engine is misfiring, -possibly-. Like it loses one cylinder at idle. That's the only way it would be "shaking like a leaf" at idle with or without AC on, with or without brake on.

I will go out and check mine at idle, brake on, AC on and see if it shakes. And report back here. If idle rpm can be adjusted up or down a tad then that would perhaps stop the shaking, if this shake is due to some sort of torque reaction sensitive to frequency-resonance of the motor mounts (is such a thing possible here? hmmm)

A four cyl. missing on one cylinder is a terribly rough running engine.

IF the engine runs fine under load but not at idle then I will guess... (guessing!) there is an ignition problem.

IF the engine rattles at idle and runs weak, rough under load then first thing to expect is a bad plug, a fouled plug, or a failed unit coil.

-just my guesses I might be wayyyy off. But clearly that "shaking like a leaf" has nothing to do with loose-anything unless a MOTOR MOUNT were unbolted or something weird like that.

 

If this engine is missing on one cylinder, you can almost guarantee a CEL.

Check the various things mentioned for tightness, check the fuel line, check your muffler. Mine needs a periodic tightening or it starts to touch the lip and vibrates.

I think that when the engine is at idle speed and the A/C is on, it pulls the idle down too slow and that's what causes some roughness.

Remember, it could be any of these suggestions, all of these suggestions or something completely different. It's mass production...

Good luck, update us if you find a solution.

 

mine makes that same noise the dealer said nothing was wrong... my co-worker and i check it ourselfs with another xb with same miles they both have that rattle noise but we r pretty sure that it's coming from the intake manifold.. didn't get enough time to open up the cover but will try when there's time

 

I am a car buff from wayyyyy back, and I HATE rattles. Mine had what you are talking
about, so I traced them down. My car is now as quiet as a sewing machine, in gear or
out of gear, ac on or not....its quiet!

The main culprit is the CAI, it shakes alot when in gear at idle. Any hose or wires
that are in contact with it will sound like a rattle from the inside of the car. Isolate
anything that touches the intake in any way and use foam rubber pads, plastic ties,
whatever, to silence the culprits.

Do the same search and destroy where the heater hoses come thru the firewall (and
under or up against the strut brace if you have one).

I eliminated all rattles in mine by doing the above.....I hated sitting at the stop
light and hearing a rattle..........good luck!

 

The symtops from the original poster resembled what I had before. At a light it would rattle away. But once the car is moving no more rattles. Went to the dealership. The adjusted the hood bumps (black looking cylinders). They may have raised or lowered it. Not sure. No for the past 28K miles.

 

Made the same adjustments in my driveway. Good results.
I can't wait for cold weather though - I suspect the interior is going to be full of rattles.