Rattle after headers installed
 

Got all my mods done & everything is great, but on cold start up it rattles. After it warms up in a few min. everything is fine. I've checked everything & the sound is coming from the rear of the exhaust. Is this the NPP or AFM valves. What can I do to fix this?

Could be either one or both. They are known to rattle. There is a epoxy fix for the NPP valves but it seems hit or miss. Best bet is to buy a X pipe, axle back, and replace the stock stuff. Factory NPP sounds good until you start changing stuff with it, then it tends to get raspy and rattles with any change in exhaust flow. Borla makes a X pipe with resonators that will help keep the sound under control if you have cat less headers.

Great! Yes I have cat-less headers, guess I'll buy the rest of the exhaust system?
Do I just need the Borla X-pipe without the AFM valves & do I need to add the mufflers with or without NPP also. My tune is with AFM tuned off, I think the NPP is still in the tune.

Is your exhaust touching the center cross member now?
I actually had to remove mine after the full exhaust install as even shimmed it barely touched when cold

Im gonna try to weld a little nub of metal up against that ceramic part in the tip. I’m thinking to get rid of the slack in the valve. The epoxy didn’t work for me long term

I did not think to check that, good idea. I will check & I think it is lower now after the header install.

You can buy the X without AFM since you no longer use it. The NPP part is up to you and depends if you still want to be able to close the valves for a quiet mode. I just did the Flowmaster NPP Axle back and it fixed my NPP valve rattle. I like the sound as well...nice and tolerable with no drone closed, but loud when open. My AFM valves were barely used far as open/close so they don't seem to be making any noise. The general consensus is the more those valves have opened/closed, they tend to loosen up and make noise.

My recommendation if you want all Borla is to get the resonator X and Sport(Not Attack) axle back since you have headers.

As JonD mentioned check your crossmember for clearance as that will cause a rattle you describe before getting too carried away.

Awesome, thanks guys!

I got it wrong, it's the DOD that is disabled in my tune not the AFM valves. I was told I need a new tune if deleting the AFM valves. I want to retain the NPP & found a Kooks X-Pipe to go with my Kooks headers but it does not have the AFM valves. If I install the x-pipe without the AFM valves what will happen?

DOD and AFM work together. So if it's turned off in the tune then the valves are not functioning. If you delete the AFM valves, then all you need to do is select disable in the fscm controller via hptuners...this will keep from getting a cel.

I see where the DOD is disabled, what is "fscm controller"?
Do you know where I can find this to disable, I'm still learning on my hptuners.

It's under "System" tab. Should see a list of options for the exhaust...one will say AFM valves enable/disable.

Not there, can't find anything to disable AFM. I think I need to buy a credit to unlock the FSCM so I can disable AFM

Yep you have to license the FSCM controller, but you should be able to read it and see the options before licensing
I would update HPT to the latest then read entire system(ECM/TCM/FSCM)