[JeffJo]

Here is a video from a clutch manufacturer explaining that there is nothing wrong when this sound is heard.

The multi-plate clutch looks much like a a container of blank DVDs. The odd numbered disks are geared to the rod down the center of the stack, and the even numbered ones are geared to the sleeve around the stack.

When pressure is applied to the stack (14:10 in the Weber State video), all of the disks rotate together. When the pressure is released, the odd- and even-numbered disks rotate separately.

The point of the analogy is that the connection is through gear teeth on the inside rod and outside sleeve. The disks themselves are free to slide up and down within the stack, to release the pressure. Because they are free to slide, they can rattle.

 

[JeffJo]

Truth be told, my wifes new Lexus ES hybrid also has this characteristic as well on cold start. Also normal. Lexus, unlike Honda... actually takes time to verbosely disclose in their owners documents this and other odd sounds and effects owners can expect.

How exactly did they describe it, and what did they say it was?

I ask, because there is no part on a Toyota or Lexus Hybrid that is remotely similar. It might make noises on a cold start, but it is not this one. I even looked through an ES300H manual to see how it was "verbosely disclosed," and didn't find such a list. Or any descriptions of noises other than the likes of "loud," "abnormal" or "electrical."

 

[JeffJo]

Lexus, unlike Honda... actually takes time to verbosely disclose in their owners documents this and other odd sounds and effects owners can expect.

Lexus does not dive into the "why", only the "what", "what about it", and "it's normal".

Okay, I only searched for "noise," not "sounds." You refer to this, from page 60 of the ES300H Owner's Manual I downloaded, in section 4-1 covering the hybrid system:

• Sounds and vibrations specific to a hybrid vehicle
• There may be no engine sound or vibration even though the vehicle is able to move with the “READY” indicator is illuminated. For safety, apply the parking brake and make sure to shift the shift lever to P when parked
• The following sounds or vibrations may occur when the hybrid system is operating and are not a malfunction:
  • Motor sounds may be heard from the engine compartment.
  • Sounds may be heard from the hybrid battery (traction battery) under the rear seats when the hybrid system starts or stops.
  • Relay operating sounds such as a snap or soft clank will be emitted from the hybrid battery (traction battery), under the rear seats, when the hybrid system is started or stopped.
  • Sounds from the hybrid system may be heard when the trunk lid is open.
  • Sounds may be heard from the transmission when the gasoline engine starts or stops, when driving at low speeds, or during idling.
  • Engine sounds may be heard when accelerating sharply.
  • Sounds may be heard due to regenerative braking when the brake pedal is depressed or as the accelerator pedal is released.
  • Vibration may be felt when the gasoline engine starts or stops.
  • Cooling fan sounds may be heard from the air intake vent under the rear seat.

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I quoted the entire thing for comparison to the Honda manual. But also to show that there is no mention of sounds or vibrations specific to cold start (which is different than starting and stopping during normal operation), and no mention of rattling.

What you apparently missed is this, from page 15 of the CR-V Hybrid Owner's Manual, in the Quick Reference section prefacing the more technical portions of the manual:

• Sounds Unique to the SPORT HYBRID i-MMD System
  • When you first start driving this vehicle, you will likely hear some unfamiliar sounds, particularly when you turn on the power system, or while you are driving or accelerating from a stop. Some of these sounds are unique to this vehicle‘s powertrain, fuel, and climate control systems; others are similar to sounds generated by conventional automobiles that typically are masked by louder noises absent from a vehicle of this design. These sounds are not a cause for concern, and you will soon recognize them as normal and thus be able to detect any new or unusual noise should one develop.
• After shutting off the engine, you may hear certain noises coming from the vehicle. Here’s the lowdown:
  • Noise from Under Vehicle: This noise is caused by the vacuum pump inside the fuel evaporation leakage check module (ELCM). Depending on conditions, the pump will come on for about 15 minutes about 5 to 10 hours after engine shutoff. This noise is just normal vehicle operation and doesn’t indicate a vehicle problem.

These two manufacturers document things in very different ways. Personally, I find Honda's method more understandable, more informative, and more accessible to someone who does not "deep dive on these systems." You may not. But outside of delineating each sound, I see no useful difference in the information conveyed. In fact, delineating them makes it harder, and so less likely, to be read. And the only sound that is "verbosely disclosed" is Honda's "Noise from Under Vehicle," which is the one that I have seen the most confusion over.in these forums.

What I object to is not Toyota's methods, as much as assuming - and stating - that Toyota's are superior without actually comparing them to Honda's.

Honda could definitely learn a few things from Toyota/Lexus in terms of owner documentation disclosure on the subtle things owners, particularly new owners, will fixate on after spending big bucks on a new high tech vehicle.

And I think that Toyota/Lexus could learn a few things from Honda. Like, if it is meant for new and inexperienced owners, it needs to be stated more conversationally. And in a section of the manual intended for, well, new and inexperienced owners.