[williamsji]

The engine in the hybrids will generate different sounds than you are used to.

Reasons are several, the most significant one being the engine is tuned electronically to an "atkinson cycle" (expansion stroke that is longer than the compression stroke, via electronic valve timing controls) which boosts fuel economy some but does so by messing with combustion timing. Plus, in cooler weather, the engine control unit will set the idle speed higher until the engine warms sufficiently as well. Couple that with the fact that the engine is doing a range of things other than powering the wheels in a hybrid and you can expect a number of different acoustics from this engine compared to the older K series and the newer 1.5Ts.

Best thing here, if it concerns you is to head to your dealer, and see if you can listen to other hybrids on the lot and compare. You also could leave it with them to check and evaluate when it is cold too... but generally the best practice is to not do this... because you generally will get back "sounds normal, no problems found" when you just drop it off with a vague description of your concern.

 

[williamsji]

This topic was discussed previously and I believe the phenomenon was explained pretty succinctly by JeffJo

The CR-V hybrid - and in fact, all Honda iMMD hybrids dating back to August, 2014 (2015 Accord Plug-in Hybrid), use a wet multi-plate clutch pack to engage engine drive. Such clutch packs are known to rattle sometimes, especially in cold weather, when the input shaft is turning but the clutch is not engaged. It's called "intermediate plate rattle." There are no known issues related to this rattle, the manufacturers of them insist "the rattle is not detrimental to the operation of the clutch," and I know of no faults associated with them in the 6.5 year history of their use in Honda hybrids.

I tried to link the actual thread but failed dismally. Sorry.

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.

But I can only hear it with the hood up and standing in front of the vehicle with the actual 2.5 ICE running, because inside the cabin with the windows up.. it's an incredibly quiet vehicle inside.

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.

 

[williamsji]

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."

I know you are a technical detail person, and love to deep dive on these systems. Lexus does not dive into the "why", only the "what", "what about it", and "it's normal". Honda and Lexus/Toyota systems are clearly different, so the actual sources and reasons of noises are likely different, though the audio and vibrations characteristics are similar in nature.

Lexus devotes a sub-section in section 7 of the interactive manual titled: Sounds and vibrations specific to a hybrid vehicle It delineates a set of 10 different types of noise sources you may hear in your hybrid which are specific to the hybrid... including from the engine, the transmission, the trunk, the HV battery pack, and the rear seating area. So far I have only actually heard 4 or maybe 5 of them. Some are described as "cold start rattles or vibrations" only, others are described as conditional noises as part of normal system operation.

I won't list them all here since it's off topic and will take up needless space in the thread. Rattling and vibration from the engine on cold start being one, but is minor in my view (maybe because cabin sound insulation is so good). The most annoying of sounds from a Lexus hybrid, in my view is actually from the transmission and Lexus specifically states: Sounds may be heard from the transmission when the gasoline engine starts or stops, when driving at low speeds, or during idling. Sure enough, particularly when the vehicle is powered up or down, odd mechanical type sounds come from under the vehicle if you are standing outside it, and in poking my head under the vehicile, yeah it definitely sounds like it is coming from the transmission.

 

[williamsji]

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.

We can agree to disagree.

The Honda paragraph you quoted about iMMD noises:

• 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.

Incredibly NON-SPECIFIC and hence largely useless, in my view.

Paraphase: you will hear unusual noises from your new Honda hybrid, but we are not going to be very specific as what they are and where they originate, but we will scatter the information around in the manual like a scavenger hunt. THAT is bad technical writing.

Honestly, I find the Lexus owners documentation to be much more complete, coherent, and informative compared to the Honda owners documents. It actually follows a much better flow for the new owner looking to learn their vehicle without being lead in circles. Lexus documents are much more conversational in their style, are better laid out, flow more logically, and better illustrated compared to my gen5 CRV documents or my 2018 Accord documents. Too much jumping around and errors in my CRV manual really for Honda being one of the top vehicle producers in the world.

Credit to Honda though for producing a web based interactive manual for the gen6... because that really is the way to go if you want owners to be able to quickly and easily follow the topics and find the topic they seek. Much better than a PDF or print copy. Easily accessible to anyone with their smart phone if needed too.