What's the C# method/syntax for converting an array to a simple string?

char sep = GetSeparatorChar();
object[] toJoin = GetToJoin();
string joined = toJoin.Aggregate((x,y) => x.ToString()+sep.ToString()+y.ToString());

char sep = GetSeparatorChar();
string[] toJoin = GetToJoin();
string joined = toJoin.Aggregate((x,y) => x+sep.ToString()+y);