It is true that a house seller has to disclose neighbour disputes.
In fact on my questionnaires the seller must fill in for the buyer to read, the questions can include problems/noise with neighbours.
If the seller has complained he cannot deny there is a problem if the neighbours have not moved. But noise is subjective.
What one person classes as loud or unacceptable another person may not notice.
However, this should not be grounds for not resolving a problem. Has he mentioned the noise to his neighbour? They may not realise they can be heard.