88 cherekee inline 6 4.0 L

lately i just thought it was because of the cold because if i was to start and drive the car without letting it warm up i would here a sought of grombling, not grinding noise when i stop in drive, as it idles in drive the noise gets louder sometimes but definately consistent with me being in drive idling because if i was to shift to nuetral the noise will stop and it idles nicely what could be causing this noise any help is greatly appreciated