Is it permissible to groan during intercourse, and is it obligatory to refrain from it if one of the spouses is bothered by it?

It is permissible to moan during intercourse as long as it is not heard by others. However, if it causes harm to either the husband or the wife, then it is not permissible, due to the Prophet's (peace be upon him) saying: "There should be no harm nor reciprocating harm." Yet, if it occurs involuntarily, there is no sin in it, as Allah Almighty says: {Allah does not burden a soul beyond its capacity}.