Dishes not clean in bottom rack of Whirlpool Quiet...

Question

The dishes in the top rack of the dishwasher are coming out as clean as normal. The dishes in the bottom rack are not getting very clean at all. Dishes that have been pre-rinsed and scrubbed still have visible smears, streaks, and other dirt on them. We have jet-dry in the dispenser and ran a wash cycle with some vinegar as well. There are no unusual noises. The inside of the tub is nice and dry after the cycle is complete.