Tips for tenant disputes?

[Todd M.]

Hi,
Have one tenant that moved in a month ago consistently complains about everything; e.g. "the oven is too dirty, I need you to clean it".

This said ("the Complainer") tenant is now complaining about noise from a neighbor who moved in above about 5 days ago ("New tenant").

New tenant says the Complainer is threatening when knocking on the door telling them to quite down.

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New terriority for me, but I'm sure it will happen again, so this is good chance to learn.

What I've done so far:
I've recorded both sides of the story in my landlord log book. I've sent both tenants letters and told them to call the local authorities if their attempts at direct, respectful dispute resolution are not successful.

Any other suggestions?

More info:
For example, the Complainer has just said "noise" while the New tenant has said it's the creaking floors. Should I ask the Complainer to put in writing the nature (voices, music, creaking floors) of the noise they are hearing.

I've heard horror stories on bad tenants and have a little experience over the past 4 years. But, this constant complaining (closet smells, the refrigerator shelves are dirty, the cabinet knobs need polishing, whoops I flushed a towel down the toilet- come over and snake it for me) is getting sickening. I had a professional cleaner in their unit before they moved in! I hung their drapes.

So, in short, I'm more likely to believe the upstairs/ new tenants.

Thoughts?

I appreciate your responses,
Todd