Hello guys, please help me.

My FFRR 4.4 TDV8 (125k miles) makes a specific vibrations. Not depending on gear (P, N, D), not depending on speed (driving or when stationery), not depending on acceleration, deceleration, but only in specific rpms starting from about 800 and ending at 1200 rpm (so very often while cruising the city) and then from approximately 2400 to 2800 rpm. It comes from the front, I feel it in steering wheel, floor, pedal and very sligthly in the seat. I think it is slighty better when the car is cold, but not so sure. Other rpms it runs great, no smoke, smooth idle, great power. I was not able to find any thread with this kind of problem. Many thanks