Ditto mine too....sounds like a hole in the exhaust but only for a few minutes.
Takes awhile to warm up enough for EV mode also. I wouldn't worry about it.

 

I also hear more ( louder ) sound in the cold.

My unproven theory: resonance

You do have a "tuned" exhaust system.
The speed of sound changes with the density of the medium.
Density of all things ( air, plastic, water, metal, glass ) changes with temperature.

Colder temperatures in general = more density

More density = faster speed of sound.

Also, colder materials tend to be more rigid and will vibrate at a different frequency.

Also, the ice in the tailpipe idea has merit. A tiny amount of frozen water will change the resonance frequency, by changing the mass. A little is all it takes.

P.S. this is similar to how BOSE ( and others ) get incredible bass out of tiny speakers. If you have some, tape a small mass like a penny inside the speaker box, and your sound may change dramatically for the worse.

 

Sorry, I've to got to kind of disagree. BTW I did noise and vibration development for 25+ years for one of the Detroit 3 automakers.

You are correct that the exhaust system goes into a structural resonance. (But this is not an acoustic resonance issue, which is why the change of the speed of sound with temperature doesn't enter into it here). The exhaust system is bolted to the engine and vibrates with the engine. The rubber exhaust hangers provide much less isolation as they stiffen in the cold. The stiffer isolators cause more of the vibration to be transmitted to the body where it is amplified by vibrating the body panels, which act like a speaker cone, thereby generating the added noise.

It is not true that a small amount of mass (ice) will change the resonant frequency significantly. Resonant frequency is proportional to the square root of K/M where K is the stiffness and M is the mass. So as mass increases, you are only seeing the effect of its square root (i.e. much less).