Aw, Mr Pipes (or may I call you Ged?). The mystery of joining in or not... Many of the poorest performers get strenuously joined in with. Perhaps that's telling you something. Maybe they prefer to hear you clearly...?

...then again I know of a singaround where everyone mysteriously finishes their beer and needs a refill when a certain turn comes around.

(Sorry Ged: good joke, really: but it did raise an all-too serious (and dull) side issue)