I noticed louder sounds from ICE. It is -10 Celsius degree in my town and it happens usually when car is stopped or barely moving. It's probably heating battery. Yesterday I noticed that this sound appears when arrow showing what powers what is showing from ICE to hybrid battery.
Is it normal?
I can say exactly when ICE charges hybrid battery because engine sound is much louder. I'm little worried.
Tomorrow I'll take closer look to that in garage. What can I check or do by myself to be sure nothing is wrong?

From what I recall it's normal.

That's comforting news. It's good nothing is wrong, but unlike a Lexus.

Completely normal, and normal for all Toyota/Lexus hybrids. You will notice this much more in the cold and you have the interior heater on. Using the interior heat is the main reason this happens. When the vehicle is stopped, normally the engine is off. But the engine is the source of heat for the interior so having the inside heater on will cool the engine too fast so the engine starts. But instead of just letting the engine idle and waste gas like a conventional car, it will use the opportunity to both warm the engine faster and add charge to the battery by running the engine rpm above idle. More efficient overall and not someting that matters to a conventional car where the engine runs all the time. If you turn your interior heater off, or turn "Eco Mode" on, you'll find this happens much less often (and almost never in the summer).

Sometimes for instance, when I go through a coffee shop drive thru, I will turn the interior heater off just while I'm waiting in line. Lets the engine shut off for the couple minutes I'm in line. I just let the seat heater keep me warm. When I exit the drive thru I'll turn the heater back on

Thank you Droid13 for your explanation. I understand it.
It wouldn't be problem if it wasn't so loud. It's Lexus. It should be quiet.

Maybe you should try turning the heater off as someone did/suggested and see how the engine behaves.

I've tried. Droid13 is right. ICE warming hybrid battery is making that loud noise. But I don't have problem with ICE warming battery, but with noise that it is generating. It is much louder than ICE making wheels move. I just wonder if
no roller, pulley or belt is used and making that noise.

There really is no reason for it to be really loud. Certainly there will be a higher sound level when if the engine is running faster than low idle, but there is nothing extra happening when the vehicle is nearly stopped and the engine is charging/warming compared with the same thing happening going down the road. But there are 2 reasons why it could seem to be louder. a) when stopped or slow, often in this case you may be very close to other vehicles, in a garage, or near walls from nearby buildings. The reflected noise in this case can make the engine noise seem many times louder than it normally is. b) the second reason is not easily able to hear the violin player in the symphony. When driving down the road, tire noise, wind noise, engine noise all blend together in a symphony. Engine noise becomes less obvious., just like its not easy to hear the one violin player among many. But when stopped, all other sounds muted, the sound from one source becomes a lot more obvious.

Thank you for your violin metaphor
Sound of ICE warming battery is twice or triple louder than ICE idle. That is what's worrying me.

I’ve also experienced the same thing in an opposite situation where my AC is blasting on a hot day and I’m queuing up in traffic. When the engine kicks in, you feel a sharp jolt in the car. It’s very disconcerting given how refine it usually is!

My understanding is of what I researched about gas engine loud sound is that when the vehicle backup the gasoline engine purposely turns loud as a safety precaution in order to make aware surrounding that this otherwise very quite hybrid vehicle is moving, at parking lots or elsewhere.