You have the best designed fully automatic machine for home or office. The clunking sound can be due to brew drive gear damage. One or more gear teeth may be chipped or broken and slipping.
To fix the machine the brew drive gears have to be replaced. The set of two gears can be ordered from the two links included below.
For regular maintenance of all espresso machines,
1- Download the document "Espresso DOs & DON'Ts" using the page link included below and review the information as suggested. There are a number of illustrated technical guides, on the page "Espresso Maintenance". I have added the link below.
Every espresso machine, Home or commercial model, is as good as the attention given to its maintenance. I have included links to
Services Unlimited Inc Parts Guru Services Unlimited Inc Parts Guru
Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/edward_bbd2c7ff4ee1828a