Rav Yitzchak Zilbershtein, rav of Ramat Elchonon neighborhood of Bnei Braq was asked if the groups of people who go to the hospitals top bring cheer to patients by playing music, singing and dancing can contiue doing so during the Nine Days or if they should not play live music during these days of mourning over the destruction of the mikdash?

Rav Zilbershtein responded that the gemara says nothing is more important than pikuach nefesh, and bring cheer and joy to sick people is a great mitzva. Also, we find that joy and happiness helps the healing process.  So it is a great mitzva to go tot he hospitals and play music and sing and bring joy to the patients who have serious illnesses even during these difficult days of mourning...

source: Haredim10