For me it's a tell-tale sound...
I started my career as an electronics engineer, so the sound of a PWM controlled brush-motor is no bother to me. When applied to my TS55, it's indeed an "expensive" rattle sound. I trust Festool has engineered the gearteeth to take the impulse load easily, so I don't really care.
But whenever the same sound occurs under load, I'm in trouble. I mean the rattling sound, there's almost always a slight "irregularity" in the sound, due to motor-control when not under absolute maximum load. If I hear even a hint of the "rattle" , it almost always means that my cut will be good.
That's reason enough for some strong language, for I've got used to the cuts being perfect.....
In my case it usually means that I have to reset my LA.... I'm from Holland, and I have purchased my TS55 as part of a CMS-TS55 set, and I purchased the LA as well, - just a rip fence, basically. It's an OK piece of kit, but the compact size of the CMS together with the ability to clamp the fence on both sides of the table AND the extra adjustment at the front end mean that there's room for some error - trust me to jump in. The adjustability of the LA fence is a great feature, but the mechanism neccisarily introduces some play and thus room for ( user) error.
My TS55 has been adjusted to have an ever-so-slightly toe-in when used on the guide-rail, but for what I do the spent part is on the other side when used in the CMS and if I am a bit sloppy, there's a chance to mis-set the LA rip-fence on my CMS so that the resulting cut is made with a slight toe-out....
Whenever that's the case , I sometimes experience the "rattle" sound, and the resulting cut won't be glue-ready, at least not in my book. Sawmarks are a no-go.
The sound may also tell me that I forgot to pay attention to the correct saw-depth. When the sawblade protrudes for more then the depth of a complete tooth the saw is kind enough to politely inform me with a slight variation in sound.
No it doesn't exactly sound nice. Cuts nice though....
So I choose to treat what some may consider to be a bug as a feature. I've made a LOT of panels glueing up discarded oak floarboards, ripping of the tongue-and-groove parts. When the first board passes and the sound is OK, I happily feed the next 30-or-so, knowing they will all be OK.
In an ideal world, I wouldn't have to worry about this. But then again a CMS is a nice kit, but it's more like a contractor's saw than a tablesaw, and the LA ( due to the size and mechanical constraints ) is not a Biesemeyer fence. And I can also fit My OF1010 in it, or use the TS55 as-is, on a rail or on my MFT-3, and the OF1010 also fits the rail, and... and... and....
Regards,
Job