No idea..... I have a 4 day old 516 and have heard no sign of popping or other anomolies. Mike, W9WIS -- Michael Melland, W9WIS Winneconne, Wisconsin USA EN54pc qrp-l #1656 - qrparci # 9875 - iparc #252 ars #1075 - http://webpages.charter.net/w9wis/