Hawkeye2

Installed PPC headers, Y pipe, Random Cats and Borla. After the header
install I get a rapping type sounds that varies with the RPM. It's not
a leak, I've checked all connections. I don't see any clearance issues
under the car. The only thing that I can imagine it is - is the AIR check
valve. However, there is no noise while in neutral. The engine must be under
some type of load to have the noise. No noise under mild acceleration,
however when moderate to hard accelaration you can really hear it.

A friend driving beside me could hear it from inside his car. Does the
AIR check valve noise depend on load of the engine? Any drawbacks to
making a restrictor plate for both sides?

Thanks.

JamRWS6

Can you explain the noise in a different way? Is it a ticking noise or a vibration?

I just made the AIR restrictors for mine and I really couldn't tell too much of a difference. I think most of the ticking noise is just the exhaust gases pulsing in the primaries which since they are much thinner than the stock manifolds you can hear them more pronounced.

Also, do you have ticking from an exhaust leak?

Hawkeye2

Not really a ticking sound, more like a rapping as if you vibrate your tongue
off the roof of your mouth! (sorry for the description) I've met other owners
of LS1's with same noise, different header brand, and others with no noise.

The restrictor plates are easy enough to try, just doesn't sound like a leak
or a ticking sound. If I open the hood and work the throttle manually there
is no leaking sound or ticking sound. It must be under load. And, if moves
with the RPM of the engine, so I don't think it's hitting the floor or the
sub frames, that would not vary exactly with RPM, and would be more
of a bang. The only other thought I had was the driveshaft hitting the
loop I installed at the same time, but there are no marks on the shaft at
all???

S2002S

I'm still having some minor leaks with the cat connections, and I suspect I have a clearance problem somewhere because under some conditions, I think I can feel/hear a slight knock.

Hawkeye2

Just finished with AIR restrictor plates, and.............................the noise
is gone! I'm one happy dude! Thanks to the how to section!

JamRWS6

Glad it worked out for you. The noise I was hearing was also a 'under-load' noise so it couldn't be heard while the car was standing still.

S2002S

What are AIR restrictor plates???

JamRWS6

AIR Restrictor Mod