Støynivået måles mandag morgen for å se om nye regler har effekt.

The -et ending is the definite article for neuter nouns.
• støynivå = “noise level” (indefinite)
• støynivået = “the noise level” (definite)

måles is the present passive form of måle (“to measure”). The -s suffix makes it passive: “is measured.”
• måler (active) = “measures”
• måles (passive) = “is measured” / “gets measured”

In Norwegian time expressions with days + parts of day, the preposition is often dropped:
• mandag morgen = “(this) Monday morning”
If you want “on Monday” generally, you say på mandag. Combining both as på mandag morgen is possible but uncommon.

for å + infinitive expresses purpose: “in order to…”
• for å se = “in order to see” / “to see”

Here om means “if” or “whether” in an indirect question.
• om nye regler har effekt = “if new rules have an effect.”
You wouldn’t use hvis (“if” conditional), because you’re not talking about a condition but about checking a fact.

In subordinate clauses introduced by om, Norwegian uses Subject–Verb–Object order (like main clauses):
• nye regler (subject) + har (verb) + effekt (object)
Unlike German, the verb does not go to the end.

nye regler is indefinite plural: “new rules” in general.
If you meant specific rules already mentioned, you would say de nye reglene = “the new rules.”

ha effekt literally “have effect,” i.e. “be effective” or “produce results.”
You could also say virke (“to work”) in this context:
• for å se om de nye reglene virker = “to see if the new rules work.”

• mandag morgen = a specific Monday morning (e.g., upcoming measurement).
• mandag om morgenen = habitual/general (“on Monday mornings,” every week).