pump problems???

Hi,
My dishwasher made a strange noise a few months ago then quit making the noise. The noise returned recently and we noticed the dishes on the top rack were not coming clean. The bottom dishes are clean as usual. We’ve checked for debris and blockage and found none. I was wondering about pump or impeller replacement. The part diagrams show one could purchase the motor and pump assembly together or just individually. I don’t now which way to throw the money, or am I going down the wrong road.
Thanks