Die klemmende Türklinke stört mich mehr als der laute Rollladen, weil ich die Tür kaum öffnen kann.

Because klemmende is an adjective-like form that has to take an ending.

Here, klemmend comes from the verb klemmen and works like a participle adjective, meaning something like sticking/jammed. When it stands before a noun, it gets the normal adjective ending:

• die klemmende Türklinke
• der klemmende Rollladen
• ein klemmendes Fenster

Since Türklinke is feminine and the article is die, the adjective ending is -e.

In this sentence, klemmende means that the door handle is sticking, jammed, or not moving properly.

It does not mean that it is physically pinching someone at that moment. It describes the handle as faulty or hard to operate.

So eine klemmende Türklinke is a sticking/jammed door handle.

Because stören takes an object in the accusative case.

The basic pattern is:

• etwas stört jemanden = something bothers someone

So:

• Die Türklinke stört mich. = The door handle bothers me.

Here:

• Die klemmende Türklinke = subject
• mich = accusative object

That is why German uses mich, not ich.

Because in a normal German main clause, the conjugated verb usually comes in second position.

The sentence starts with the subject:

• Die klemmende Türklinke = position 1

So the verb must come next:

• stört = position 2

Then the object follows:

• mich

So:

• Die klemmende Türklinke stört mich ...

This is standard German word order.

Because this is a comparison between two subjects, not between two direct objects.

The full idea is:

• Die klemmende Türklinke stört mich mehr, als der laute Rollladen mich stört.

The second part is shortened, and the repeated words are left out:

• ... mehr als der laute Rollladen

Since der laute Rollladen is understood as the subject of the omitted clause, it stays in the nominative:

• der laute Rollladen

Not accusative:

• den lauten Rollladen

mehr als means more than.

It is comparing how much two things bother the speaker:

• Die klemmende Türklinke stört mich mehr als der laute Rollladen.

In other words:

• the sticking door handle bothers me
• more than the loud shutter bothers me

This is a very common comparison pattern in German:

• X ist wichtiger als Y.
• X nervt mich mehr als Y.
• Ich mag Kaffee mehr als Tee.

A Rollladen is an exterior roller shutter or rolling blind, common on houses and apartments in German-speaking countries.

It is not the same as a light indoor curtain. It usually refers to a heavier shutter that rolls up and down outside or in front of the window.

So der laute Rollladen means the noisy/loud roller shutter.

Because laut is an adjective placed before a noun, so it needs an ending.

Here we have:

• der laute Rollladen

Since:

• Rollladen is masculine
• the article is der
• the noun is nominative singular

the adjective takes -e.

This is the same pattern as:

• der große Hund
• der alte Tisch
• der laute Rollladen

Because weil introduces a subordinate clause, and in German subordinate clauses the conjugated verb goes to the end.

Main clause:

• Die klemmende Türklinke stört mich mehr als der laute Rollladen

Subordinate clause with weil:

• weil ich die Tür kaum öffnen kann

At the end of that clause, you get the verbal part:

• öffnen kann

This is normal for German subordinate clauses:

• weil ich müde bin
• weil er keine Zeit hat
• weil wir nicht kommen können

Because this is a structure with a modal verb.

• kann = can
• öffnen = open

In German, when you use a modal verb, the main verb usually appears in the infinitive. In a subordinate clause, both go to the end, with the infinitive before the modal:

• weil ich die Tür kaum öffnen kann

Compare:

Main clause:

• Ich kann die Tür kaum öffnen.

Subordinate clause:

• ..., weil ich die Tür kaum öffnen kann.

Kaum means hardly or barely.

So:

• ich kann die Tür kaum öffnen means
• I can hardly/barely open the door

It shows that opening the door is possible only with great difficulty, or almost not possible.

Other examples:

• Ich kann kaum schlafen. = I can hardly sleep.
• Man konnte ihn kaum hören. = You could barely hear him.

German often repeats the noun when that sounds clearer or more natural.

Here, die Tür makes it very clear what cannot be opened. A pronoun would also be possible in context:

• ..., weil ich sie kaum öffnen kann.

But die Tür is more explicit and avoids any possible confusion, especially since the sentence also mentions a Türklinke.

So using die Tür is completely natural.

Yes. Türklinke is a compound noun:

• Tür = door
• Klinke = handle/latch/door lever

Together:

• die Türklinke = door handle

German uses compound nouns very often. The last part usually determines the gender, so because die Klinke is feminine, die Türklinke is also feminine.

Yes, but then the structure and meaning would be different.

For example:

• Die klemmende Türklinke stört mich mehr als den lauten Rollladen.

This sounds incomplete or odd by itself, because it suggests a comparison between how much I am bothered by the door handle and something happening to the loud shutter as an object. Native speakers would usually not say it this way here.

The nominative der laute Rollladen is the natural choice because the sentence means:

• The sticking door handle bothers me more than the loud shutter does.

So in this sentence, der is correct.