Three different sounds for one written ending
One written past ending, three spoken sounds - and the simple rule your mouth already wants to follow.
We walked to the station, played cards on the train, and waited an hour for the bus.
The regular past ending is written one way but spoken three ways, and the last sound of the verb decides which. After a voiceless sound - one made without the vocal cords vibrating - the ending is a short /t/. After a voiced sound, including all vowels, it is a short /d/. Only when the verb itself already ends in a /t/ or /d/ sound does the ending become a full extra syllable, /ɪd/.
The classic error is pronouncing the ending as an extra syllable on every verb, because the spelling suggests one. That extra syllable exists only after a /t/ or /d/ sound - everywhere else the ending is a single quick consonant glued to the verb, and inserting a vowel there instantly signals a learner accent.