Does anybody know what is problem when you have rpm's in range of 1200-1400rpm you hear vibration sound? For example driving 60km/h and vibration sound can be hear?

If you slowly accelerate it starts to vibrate when rpms are ~1200rpm and going stronger ~1300 and disappearing soon after 1400rpm.

In fast acceleration it is difficult to hear. Maybe it is so short time when it passed through this rpm range or it does not happen.

Sounds like when turbine lock is enabled (?) in that rpm range and then sound is coming. Or it is exhaust resonance or what?

Any idea where this comes and how to fix it?