buy a new mongoose, and if it starts rattling send it back!!!

thats what you pay.

i've not had problems with mine.

sayin that it did sound like their was a bolt in it but turned out to be the wastegate partly open.

it has a little penny like flap that is riveted on and when i backed the actuator off to regulate the boost it rattled.

not that that will be your problem if you've not messed about with yours.

turned out my amal valve was shot!!!