Wastegate chatter doesn't exist the audible chatter is nothing more than the compressed air being forced backwards through the turbo whilst the blades are still trying to compress air when the throttle butterfly is closed.
A couple of quick videos of chatter taken from my Fiesta RS Turbo
http://uk.youtube.com/watch?v=baUEBAKw5vQ
http://uk.youtube.com/watch?v=ts6_ZCjtLUQ
RS Turbo's do not need dumpvalves to operate safelt but our A4's do due to running a MAF based engine management system. If you shut the throttle and force air the wrong way the MAF has the air passed across it and can't distinguish the direction and over fueling occurs. I've also been told the K03/K03s turbo's are a bit more brittle than the Garett items used by Ford but don't know hoe true this is. I know my other RS runs at 25psi of boost and runs no dumpvalve at all and hasn't for years
P.S. <y Forge valve makes a funny ptsh ping noise