Vibration after 65mph

[Aldo ko92]

Hello guys so I have a 2011 Mercedes c300 4matic and the car vibrates when I reach 60-65mph and stayes to a higher speed.. sometimes the car does not vibrates at all
Mostly feels like the vibration comes from the rear end but also sometimes feels like the whole car vibrates - I have to mention that the steering wheel does not shake at all.
I do feel the vibration on my seat
Any suggestions?
thank you
Aldo

 

[Blobcat]

Rear wheels out of balance or as likely as not, “out of round“ from potholes and traffic calming measures

 

[Aldo ko92]

Rear wheels out of balance or as likely as not, “out of round“ from potholes and traffic calming measures

Thank you
I thought about it too but if the tires were out of balance - wouldn’t the car vibrates all the time?

 

[Blobcat]

Thank you
I thought about it too but if the tires were out of balance - wouldn’t the car vibrates all the time?

No, the imbalance can have a “resonant frequency” that only shows up at certain speeds

 

[Aldo ko92]

No, the imbalance can have a “resonant frequency” that only shows up at certain speeds

Right I agree
But what I meant was that the vibration sometimes is not even there even if I do 65,75mph or higher speed
You know what I mean? Like the car does not vibrates every time I reach 65 mph or more. And the vibration sometimes is worse sometimes is slight and sometimes is not there at all. If that makes sense. Thank you