I have a used set of Fast Intentions RTP's (~10K miles) mated to a custom catback, pictured below, and for the first 5-10 minutes of every drive I have to keep the car under 2500rpm or else I experience a metallic-y rattle sound coming from the test pipe area. Once the exhaust is good and hot it goes away, but on a cold start it sounds like trash.
The resonators on each of the test pipes had a gash in the perforated pipe, and you could hear the packing was a bit loose in one of them before they were installed, but I figured this wouldn't be a problem. Are all test pipes or resonated test pipes like this? I know what rasp sounds like and this is more tinny and metallic, so that can't be it.
Looking for some input.