So even if the noise is happening on start up for like 10 seconds, I'd still tell them I can hear the noise upon throttling or just off idle? Is that the only way to get them to actually check the turbos? lolYes, wastegate rattle IS NOT normal and is absolutely grounds for replacement.
What they're doing is looking at the manual where there is a note that specifies that "noise from the area of the wastegate" isn't a malfunction. The "noise" it's referring to is exhaust noise, not rattling but since it's not specifically defined, it's open to interpretation.
Any competent technician will know that wastegate rattle is a problem. Eventually, it'll throw a code when it gets bad enough but the problem is that you'll notice the performance loss long before that because of tolerances. IIRC, the wastegste has a range of like 8mm. The fully open tolerance is a full mm and the fully closed is around 0.5mm. It takes a lot of shaft wear before the ecm gets tired of compensating for anything in between.
Take it back and tell them you notice a loss of performance and that you hear a distinct rattle noise just off idle, like if you can hear it anytime in neutral and you lightly apply throttle or when you take off smoothly from a start, hot or cold. Tell them it didn't make this sound new and it makes this sound anytime them.