Hello and Welcome -
My name is ***** ***** Im happy to help / advise. Im sorry to see you have had a wait.
Given what you describe, Im assuming you have checked the usual already, such as out of balance wheels / damage to any of the wheels / tyres / condition etc...
If you rule these things out, have the drive train checked out - by that I mean, the drive shafts / joints especially - these are known to cause such vibrations.
Too - check / have checked the exhaust system - you can get the baffles failing inside the silencers and also the cat converter failing - such will cause vibration noises.. not vibration of the car, but noises. The rest as mentioned above, will cause vibration of the car on the road. Check too , the engine and transmission mounts - and the bushings for the suspension.. both front and rear.
If all else is checked and passed, then I would suspect a flywheel fault - on a manual transmission ...
One way or the other working through as above, the fault / cause should be found. Its not at all easy sometimes to find such faults - but those are the items to be checked for sure.
Let me know how you go..and / or let me know if you need anything further on this..
~>>~~>>~ Meanwhile now - Please do click on the "Exc / Ok rating" for me at this time.. "Thank you" in advance for that .
.. Note that you can get back to me anytime at all after doing the rating - it doesn't close you out --
Best Rgds, MIKE.