Is singing during the Lord's Supper scriptural.
There are no scriptures that suggest that singing during the Lord's Supper is something that the early church did. In 1 Corinthians 11:23-34 Paul gives the pattern that we are to follow when observing the Lord's Supper. One of the things that he says we are to observe is in verse 33, "Wherefore, my brethren, when ye come together to eat, tarry one for another." The idea here is that we are to be careful to allow each individual the care and time in order to partake and reflect upon the death of the Lord accordingly. I do not think that this could be done while the church is engaged in singing a song. By necessity, when partaking of the Lord's Supper, one would need to be partaking while another was singing. One would not be able to sing while another was singing. In essence, this would be contrary to the spirit of unity which Paul commanded the church to have in 1 Cor.11:17-22. If one is partaking of the Lord's Supper and another is singing, then are we united in our thoughts and actions (1 Cor.1:10)? We would not be. There is plenty to occupy a persons' time when partaking of the Lord's Supper in reflection upon the Lord's Supper; we need not sing. Adding an additional element such as singing only serves to confuse and divide. Let everything be done decently and in order (1 Cor.14:40), and in a way that would serve Christian unity, not disunity.
So, because 1) the scriptures do not reveal this practice, 2) we are told to wait on one another, 3) each individual needs time to reflect personally, and 4) we must do things decently and in order, my conclusion is that it is not a scriptural practice.