rsimons

Considering buying one to get rid of the annoying DFM noise. Can you confirm if this also eliminates the noise at cold start, or just on decel / downshift?

Quick follow up. I just tried the L9 mode and confirmed that it stops the noise while driving (decel). Of course this doesn't help on cold start while in Park. Can anyone confirm if the Pulsar LT (DFM deactivation) will help at start up?

I have the exact same issue on my 2021 Denali 6.2L. I do not have the performance exhaust option. Dealer first told me it was the butterflies in the exhaust and that it was normal. I then installed a Magnaflow exhaust that eliminates them. Still makes the noise. Brought it back to the dealer, and they said they drove another truck and it makes the same noise so it's normal, but couldn't tell me what it was. I called GM customer service, and have been going back and forth with them for almost 3 months. They finally told me to make an appointment with the service manager to drive a similar, new, vehicle and see if it makes the noise. 3 weeks of trying to get in touch with the service manager and still no calls back. The noise is really annoying.

I have the same problem on my 2021 6.2L Sierra Denali. 1st time I took it to the dealer they said it was the flapper valve and it was normal. I then installed a Magnaflow cat back, but it still does it. Took it back to the dealer and they said they drove another one that made the same noise so it's normal. I asked what it was and they said they don't know. It sounds like an exhaust leak, but they said there where no leaks. It does it bad at cold start, and also on decel, right before you come to a stop. Also, sometimes on light acceleration.