4th motor in our fridgidaire?

About 4 months from new, the circulation motor in our Frigidaire FDB520RMS2 quit working. I called customer support, they sent a replacement motor, which I installed. New motor was immediately louder, by the 3rd time we ran the dishwasher, it was obvious something was wrong. The circulation motor makes a groaning noise that gets louder the longer it runs. It will ‘reset’ to relatively quiet when it stops for the brief periods during the cycle. Called support again, they sent another motor, said the first replacement may have missed quality control?? I installed the 3rd motor, but now it is about a month later, and the noise is returning. I checked to be sure there is nothing obstructing the impeller or grinder. Support wants to send another motor, but I am concerned we are overlooking another (underlying) issue. The original motor never made any unusual noise. Is this a common problem with this brand or model? Can you help me with any ideas on how to get a fix for this?