DGX-660 right speaker rattles on specific notes

Hello all, I’m new to the forum. A brief introduction: I’m a long time self-taught “keyboard jammer” (“player” would be too much!) from Italy, but I enjoy fiddling with other instruments as well; the most recent one being electric bass.

I’m posting here in hope that someone can guide me towards fixing an odd issue on my Yamaha DGX-660. While I have experience with repairing things, I’ve never performed any surgeries on keyboards and I wouldn’t want to turn a small issue into a huge mess.

My 660 only left my house for a couple of trips to a nearby repair shop shortly after I bought it, several years ago, since the metronome LED was only flashing red and not green. After that, it just stayed on its stand and I never took it elsewhere, so it never received any hits or bumps or anything of the sort.

It sat there for a while as life got in the way, but I’ve been playing it more lately. However, I noticed that the right speaker rattles when I hit specific notes using specific voices, most notably (and annoyingly) the pianos.
In particular, that happens with A4 (to be super-clear: the A just below the right edge of the screen), occasionally with G#4, occasionally with A3, using virtually all piano voices and a few others here and there.
It doesn’t keep rattling for the whole time the note is sustained, it’s more of a “frrrr” sound during the attack, and it gets worse as the velocity or volume increase. I was able to confirm that it comes from the speaker because pressing down on the grill with a finger or two is enough to make it stop. Lightly touching on it actually lets me physically feel the crackling, if that makes sense. I also confirmed it with a spectrum analyzer app (hey, I am a nerd.)

Does anyone know how these grills are actually mounted to the rest of the piano? My hunch would be to try and re-seat the right speaker’s grill to make sure it doesn’t move, but I’m not sure how to approach that. The screws underneath the whole unit seem quite tight, but none seem to be holding the speaker grills in place directly.
I found this video of a repair on youtube but the grills are not touched by the author, and it’s not very clear how they’re mounted. The closest view I could get is at 5:54, but there seem to be no screws whatsoever, just some odd diagonal “tabs and slits” that I’ve never seen before (I enhanced the contrast in this screenshot):

Can anyone provide any tips on how I could approach this? It’s really quite annoying to get that rattle every time I hit that A key.

Thank you everyone in advance!

I would carefully compare the right grille to the left one. The solution may be as simple as a small dab of glue.

I can’t see any difference between them. They both seem to be whole, without any cracks, and trying to “shift” them in place offers the same amount of resistance. Maybe I’m misunderstanding your suggestion, though — what should I be looking for?
Thank you very much for your input!

It may not be the grille. Rattles can be tricky to pin down but the fact you are able to stop it by pressing with your fingers is a good thing. It could be an adjacent part that is influenced by the pressure you place on the grille. It may take some trial and error but eventually you will find it.