not even in the plastic tube, but just floating around freely inside the nozzle directly under the red screen

Hey, to those with the ZS3. I found a new mod tonight.It has been previously posted by a few people that removing the red screen on the very end of the nozzle affects the sound. Removing it reduces the bass quantity slightly (while simultaneously removing the muddiness), and also improves the midrange.BEHIND the red screen is a small piece of black acoustic foam. It's stuffed in the very tip of the plastic tube (the color of the plastic tube might be red or blue). It's exactly like the piece of foam stuffed inside of the shiny gold ED9 filter. Anyways, you REMOVE this piece of foam by just grabbing it with the tip of a sewing needle. You'll need a flashlight to assist seeing down inside of the nozzle to where the foam is. Carefully set aside the foam - they're extremely small and easy to lose. You can store the foam pieces in a small ziplock baggie like the one that many silicone eartips come in.The change is a very noticeable improvement - the boominess that the ZS3 had is now gone, upper mids are less recessed, and the treble is sparkly and clear. They kind of remind me of an improved ATR, but I need to A/B them with the ATR to verify. Synthesizers, pianos, & guitars sound great.It's tuned much more towards neutral with the mods, but there's still plenty of bass when called upon. It just isn't boomy and muddy like it was stock. Don't get me wrong, I think the ZS3 is a pretty good in-ear (especially for bassheads). I just know a lot of people are turned off by its overpowering bass that dominates the whole listening experience. This mod corrects that.It's up to you if you remove the foam yet put the red screen back, or remove both the foam and the red screen. It's easy enough to try it both ways and see which you like better. I settled on removing both after trying it both ways. Just keep an eye on ear wax buildup inside the nozzle if you run with no red screen (remove ear tip every once in a while and carefully clean out any funk).The mod is very easy, takes less than 30 seconds total, and is totally reversible.You use the sewing needle (or small straightened paper clip) for removing both the red screen and the black foam. Gently pry the edge of the red screen using the needle and it will pop right up. It's just held on by a ring of sticky adhesive around the edge. I stuck mine to a piece of wax paper to save for future keeping, as it sticks right back onto the end of the ZS3 nozzle if you ever need to put the red screen back (instead of wax paper, you could use anything non-stick - plastic wrap, sandwich baggie, or the slick paper backing from a peeled-off sticker or vinyl graphics.Here's photos of the red screen so you know what to expect:The following interior diagram will show you everything that you need to know (you don't actually open the shell for the foam mod - the interior diagram is just to illustrate where the foam is located):I found a camera lens and settings that would allow me to get a good shot of the foam. It's impossible to gauge the depth in this photo, but that foam is located about 1/4" down inside the nozzle:Here's what the piece of foam looks like after you've removed it with the needle (it gets more compressed once inside the plastic tube):Also, while you're at it you may as well use the sewing needle to verify that the vent hole is open and not blocked. Just poke it with the sewing needle (or the tip of a thumbtack) and make sure it's not blocked with glue.Something that has always bothered me about 1 of my pairs of my ZS3 is that 1 side never sounded quite right. Well, low and behold I found that the foam on the 'never quite right' side was. So at a minimum, looking under the red screens will allow you to make sure both of your foam pieces are inserted properly into the ends of the plastic nozzle. There have been reports of sound mismatches on 1 side. Early batches of the ZS3 had a crushed sound tube. Those were recalled a long time ago, so if you have a relatively recent ZS3 and you have something odd going on with 1 side, it could be that the foam isn't situated in the tube properly.Let me know if you have any questions.- SlaterP.S. - To the advanced IEM builders/modders out there, as you can see from the exploded diagram this would be an excellent host for turning into a hybrid DD + BA. The shell is easy to open, it's comfortable as heck, and there's plenty of room inside for a crossover in the shell & a BA driver inside the nozzle tube. Looking at the above photo, it almost looks as if KZ was planning that all along, and it wouldn't surprise me if a "ZS4" comes out as a dual hybrid using this same shell as they already have the shell tooling. Also, it would be easy to swap out the plastic tube for a copper one, as the plastic is extremely thin (it looks exactly like a piece of heat shrink tubing that hasn't been heated/shrunk; or it could also be a piece of drinking straw). It's that thin & flimsy.