Car vibrating at constant speed

When driving around 60km/h and just above eco mode line.
The car is slowly decellerating and i can hear the ice engine rpm drop.
Its been around -10C if that matters.

When it reaches a low rumble, probably around idle or lower, I can feel shaking in the steering wheel and hear a low rumble. Has happened at highway speed too. Always when the ice engine is at idle ish rpm and cruising.

Usually when I just need a tiny ice power to maintain speed, just barely above what EV can provide.

There are no such issues during acceleration or at idle stopped.

2013 prius c 78000km

 

I don't think its the suspension. My first gut feeling was maybe its the engine mount, but all other driving conditions are fine. Its almost like it hits a resonant frequency at that low rpm. The whole car buzzes with it.

 

Blah, I made a video to try to record the noise but the phone was on my dashboard and other rattling sounds completely mask it... Ill try again tomorrow.

 

Went back to the place that put my winter tires on. Tires seem fine and checked drive shafts. everything seems ok.

Did some more driving.
Noticed a vibration whenever ICE is around 1150-1250 rpm. This is a mild vibration and not very bad per say. This is what I most commonly feel.

However, whenever MG2 is around 7500 rpm there is vibration of similar frequency but much greater amplitude, regardless of ICE rpm.
When ICE rpm is at 2000rpm and MG2 is at 7500 the vibrating gets really annoying where you can feel it in your whole body. Its a low rpm vibration, id guess around 5-20 hertz. This is usually around 95-105km/h since mg1 is practically in sync with the drive shaft. Though, if ICE rpm is not 2000, it is not that bad. This is usually a very slight acceleration or a little bit quicker slow down, keeps ICE away from 2000. So, I am not sure if quicker speed change gets me out of the harmonic range quick enough so that vibrations don't have time to build up, or if the harmonics of the ice at 2000RPM and MG2 at 7500RPM constructively interfere with each other.

So imbalanced MG2? I read many other threads about random vibrations on here. Do you know if anyone else tracked RPMs?

In all this MG1 rpm seems irrelevant.

 

No its still that one. I made my peace with the low intensity one but then occasionally its bad at those rpms. so Im back and forth about being and not being worried about it.

I have the low intensity grumbles regularly and its fine and used those to convince myself its fine. but the high intensity ones are still worrying. Needs a very specific scenario to make it happen though, but unfortunately driving in the 95-105 range is pretty common.

 

Possible. Ill have my winter tires taken off in the next couple weeks, and then I'll know.

 

Issue is resolved.

I been mulling over everything. Bought a new pump and a high quality pressure gauge. Turns out the fronts were 25 and the rears ~20 psi...

Intense vibration is now gone. Fuel mileage has improved significantly. Weirdly the fronts at 25 psi just didnt look that low. Stupid thing.

Low intensity rumble still remains, I thin that is just normal for this drive train when generating.

Thanks guys!