Trash compactor bounces and clatters at end of the cycle (up position) It is a Whirlpool brand.

I used to have a Sears trash compactor -- believe most are similar

A motor drives a sissor type ram down -- smashes trash -- returns to top

Trash Compactor Diagnostic & Repair Guide: Free On-line Troubleshooting and Repair - ACME HOW TO.com

Take the back off compactor and operate it to see problem

Sounds like drive problem chain or gears that drive it