W123 300DT Vibration until 2000 RPM
 

I have this 1984 300D I just started driving. Drives great, turbo kicks in beautifully and gives lots of power. Strange thing is that when accelarating hard, between 1250 and 2000 RPMs there is a strong vibration/rumble in front right area of engine. Then invariable right as turbo kicks it completely smooths out and accelerates beautifully. It will do it in park too. I need to have some one rev it up while i look under car i guess. Thanks for any ideas and insight.