Learn German: Der Bademeister hört dieses Gemeckere jeden Tag im Schwimmbad. - The lifeguard hears this constant complaining every day in the swimming pool.

It comes from the verb meckern (to complain or gripe). By wrapping the verb stem in the prefix Ge- and the suffix -e, it becomes a neuter noun (das Gemeckere). This specific structure is used to describe an action that is continuous, repetitive, and usually highly annoying to the speaker.

Why does it say dieses Gemeckere with an -es ending?

All nouns formed with the Ge-...-e circumfix (like das Gerede or das Geheule) are neuter. Because the complaining is the direct object being heard by the lifeguard, it is in the accusative case. The demonstrative pronoun dies- takes the neuter accusative ending -es, resulting in dieses.

Why is it jeden Tag rather than jeder Tag or jedem Tag?

Definite time expressions that answer the question 'how often?' or 'when?' and don't use a preposition must take the accusative case. Since Tag is a masculine noun (der Tag), the word jeder takes the masculine accusative ending to become jeden Tag.

Could the word order be changed to put jeden Tag before dieses Gemeckere?