I like Dynaflight '97 and Formula 8125 for bows built to handle them. Depending on your preferances, 10-14 strands in the string with 18 in the loops (if flemish).
Generally string material won't make nearly as much difference with noise as tuning, release, nock fit, and arrow weight.
Tune with the brace height and silencer placement. More silencer material doesn't mean better--moving the silencer up or down the string an inch or less at a time can make a big difference.
A clean release is a quieter release.
A tight nock will make more noise than a light snap.
Heavier arrows are quieter. Also, arrows that are not the correct spine may slap the riser and add noise. A little tuning can go a long way.
Chad