Finally took the time to examine this problem. If you have this problem, just pry out the tweeter (very easy). The plastic grille and the tweeter (with plastic surround) come out in one piece. Disconnect the wiring connector and remove.
The tweeter and grille is a two piece assembly and it was a bit loose. The tweeter is held in the plastic grille with 3 snap on fasteners. Unsnap the tweeter and put a little silicone adhesive where the fasteners are. Snap the tweeter back in and that is it. You can use just about anything, double stick tape or whatever to tighten up the clearance.
It is a very simple solution and easy to do.

Is it the tweeter on the dash under the windshield or the left speaker on the door panel?

Thanks

Depends on your rattle. Does it stop when you slightly push the left tweeter down? Then try and push down the dash down just in front of the tweeter. Does the rattle stop again. Well, I thought I solved it from the tweeter, but it is still there, just not as bad. This is one persistent rattle. So if you get it fixed by the dealer, let me know details. Im trying to avoid the dealer, but may have to go that route. Now is your rattle sound like plastic hitting plastic?
Other people have some type of rattle on the left side of the dash.

plastic on plastic. almost sounds like a tiny piece of plastic is rolling around in a confined spot. it's not always over bumps either. it can happen over road dips or on deceleration

Hi,
Question, does the rattle starts after certain milage? I have 9000 miles on my TL... so far I've never heard of any rattles or driving vibrations yet... i have a 2004 TL..
thanks

Before you go ahead and remove the tweeter make sure that's the problem. I thought mine was making the noise but it turned out to be coming from the point where the dash panel meets the A-pillar cover. A small piece of foam jammed in the joint solved the problem. Can't even see it because the foam is black.

rattle was there from day 1

Yep, from day one. Ive done the foam between the Apillar and dash. It seems like it is just below or near the tweeter.

Tweeter area rattle non-existent for the 1st time since I took delivery of the car in December 2004. This was the 1st time i didn't use the heat (55 degrees today). Any ideas or correlation?

It is a hot/cold expansion/contraction thing. When it is very cold or warmed up to say 60 degrees, the rattle stops. But under 60, it rattles away. I have pushed down the dash and the very lower area of the A pillar and the rattle stops. So try pushing down on those areas while its rattling and see if it stops. It only takes slight pressure to make it stop. As for a permanent solution, still trying to figure it out.

Thanks tman. I have the DSM driving it next Monday. I need to make sure I re-create it for him. Is the rattle activated by the heating system in your opinion, or ambient warm temps?

It is ambient. It is not activated by the heating system or warm temps. For example, this morning it was about 55 degrees outside and the rattle was going crazy. Later in the afternoon it was about 63 degrees outside and there was no rattle at all. Inside the car was warmer then that. I can't believe a DSM has to drive your car? Your dealer couldn't figure it out?
Does your rattle sound like a tic tac in a plastic box? Sounds like a plastic fastener making all the raucous.
If you get a fix, please send all details on how they fixed it. Even if you have to talk to the service tech. Sounds like a bunch of people have the mysterious left dash rattles. Good Luck!

That's it exactly. A tic-tac rolling around in a box. I will let you know what they find next Monday. Hopefully it will be fixed.

Brought car to dealer and of course, I couldn't duplicate it while they were in the car. Rattle comes and goes. I just can't isolate it to attempt a fix on it.

did anyone answer this question

The temps were not in the cards for you. Mine is not as bad because the temps around here are going up. It will rattle badly at a certain temps though. Best thing for you to do is when it is doing it badly, go straight to the dealer if its close to do so.

rattled away all of yesterday (after driven 30 minutes), totally quiet last night (5 minute trip) I think it's right under the vin plate area of the dash. I'm going to drive it in when it's most evident. Ops Mgr. said that would be ok.

Yep, it has to be the right temps. If its too cold or too warm, its quiet. What a pain! Im sure it will be quiet all summer.

I wish I could park my car on a vibration table. That way, I could isolate all the rattles with the car sitting stationary.

In my previous car, I was able to find and fix rattles by playing a loud, low-frequency sine wave through the subwoofer. I'd slowly sweep the frequency up until it excited a rattle. I'd then track it down and fix it before continuing up. I don't think the TL's stock subwoofer has enough oomph to do this trick, but I'll give it a try and report back.

Did anyone ever fix this issue?

I am having the same problem in my 04 TL, though it's coming from near the right tweeter.

When the passenger pushes the dashboard down it stops. I don't think it's actually the tweeter, though I might pull the tweeter out to see if I can get under the dash that way to just jam in some foam.

Bump. Has anyone figured this out? I'm going crazy.

Btw, I have an 05 TL and not an 04. Typo in the previous post.

OK. another bump.
Can't believe Acura still did not fix this problem until 2008 model.
I have the same rattle on my brand new 2008 TL. Plastic tic-tac. Looks like this rattle comes from the driver side dash tweeter. Took the car to dealer 3 times. They replaced grill, replaced tweeter but the rattle is still there. Seems like the rattle goes away if I press on the tweeter grill. Does anyone has a definite fix yet? I gave up on dealer fix and decided take this matter in my hand.

I know this is an old thread but the problem still exists for people and I have a stupidly easy fix ... Get a piece of rubber like a vacuum cleaner belt and stick it up in where plastic meet plastic area up where the tweeter is located and voila the problem will be solved for you - jam the rubber piece in using a pair of scissors or a screwdriver. I had this problem on my RSX (from day one) and took it into the dealer several times and they foamed the hell out of the area and couldn't get it fixed (and foaming it won't help). Also the reason why it happens when it's colder out and stops when it's later and hotter in the day is cause stuff expands when it's hotter out ... this is also why it's so hard to duplicate cause after you've been driving a bit the car warms up... People who live in say Phoenix might be thinking this post is on drugs and never had the problem, but anyone who lives in Chicago and has their dash rattling all winter long might go insane.