My tenants have fallen out

It's the stuff of teenage fall outs, but my tenants in two adjoining flats are not speaking to each other. The tenant on the ground floor maintains that the tenant in the top floor flat is causing endless noise nuisance. This I find hard to believe having known how considerate and polite this tenant has always been with me. I received the other day this missive on the alleged audible misdemeanors of the top floor tenant. So far I have ignored it? Am I right? The missive goes like this:

 I don't know if last time you visited you had a word with TENANT X about noise but matters have not improved since. Many times since I have thought he must be moving out with the amount of noise he's been making. It still sounds like he is moving furniture regularly, banging, dropping heavy items, as well as stomping up and down stairs, banging and 'rocking' the front door...generally not considering neighbours. It can be even worse when he has a visitor staying which has been happening regularly. 

Last Thursday morning, after months if not years of not complaining (except once recently when I lost my temper in response to excessive banging in the kitchen and tapped the ceiling with a brush, only to be met with shouts of 'fuXX off'), I opened the door to him locking up and singing in the hall (following much pre-work? noise). My opening line was not ideal, I admit, as I questioned whether he was determined to disturb me as much as possible. However, his response was one of someone who could not believe the issue was being raised again, stating he was' living his life'. On asking if the noise was really of the reasonable and everyday variety I was told I was 'mad'. He repeated this accusation several times, finally concluding that I was 'absolutely mad'. I thanked him for that and he left. 

Since then he has been a bit quieter/out more so I hope the same problems will not arise again. 

Should a landlord take sides on what clearly is a very subjective issue such as noise?  Clearly there are mechanisms when it comes to noise pollution such as calling in the Environment Health Officer to assess the nuisance factor.  My approach so far is not to get involved.  I suspect to do so would only alienate myself to one or other of my tenants.  This is not something I want or need to do.

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