General annoyance:
* Annoyance: This is the most direct synonym.
* Vexation: This suggests a stronger feeling of irritation or frustration.
* Irritant: This emphasizes the thing causing the annoyance.
Causing trouble:
* Problem: This is a broader term, but can encompass a nuisance.
* Trouble: This suggests a more serious issue than a mere annoyance.
* Pest: This implies something that is persistently annoying.
Informal words:
* Pain: This is a colloquial term for something that is annoying or troublesome.
* Bother: This is a more casual word for a nuisance.
Ultimately, the best word will depend on the context and the specific kind of nuisance you are describing.