problems with Skoda Fabia 1.9 SDI 47kw

hello briskoda guys . i am from bulgaria . i wish you all the best with your cars . now i have a problem with skoda fabia SDI when i start my engine it works good without any strange noise and corectly RPMs when i start to improve the RPMs and accelerate softly i feel vibrations coming from engine only at 1000-1100 RPMs at this moment if i accelerate with full throtle vibrations mising or i dont feel.At the high RPMs does not have any vibrations what could be the reason and what i have to do to solve the problem. thank you in advance best regards friends