exhaust interior noise

[clotuning]

if im cruising in my ls1 (about 1700-2200 rpms) my car has this annoying loud inside its but outside its not that loud. my ka24de with my n1 style exhaust wasnt this irritating and neither was my civic that had a prelude engine with a magnaflow muffler and no resonator. i was doing some searching around and people were saying that the chassis metal vibrates at a certain frequency that the exhaust eventually puts out at certain rpms. im assuming this is what im dealing with.

Does anybody have any experience with certain resonators or mufflers they recommend? i currently have a magnaflow muffler and some ebay 240sx resonator and i have no exhaust leaks (tested with a smoke machine).

[Def]

The easiest thing to do for a specific frequency is a hermholtz resonator off the exhaust. It might be kinda large for such a low frequency.

You might try a big ass straight through muffler, but there isn't too much space to fit something like that on an S chassis.

[Matt93SE]

What type of engine and Trans mounts are you running? Rubber, poly, solid?

[clotuning]

Mounts are poly

I searched hermholtz resonator and came up with this photo. Have you or anyone had experience with this before?

[Def]

Yea, they're very common on stock BMWs. They knock down a very specific frequency, so you can't just guess, you need to know what frequency you're trying to cancel.

[BEXE]

You can make adjustable ones. Then you can vary length and tune it in.

[Matt93SE]

It's likely the poly mounts are transmitting lots of vibration into the sheet metal and rattling the cabin like a drum. My car got REALLY loud when I installed poly mounts on the KA and way better when I went back to stock.

[Def]

Aye - easy to do when you remove all the sound deadening tar and put some more energy through the body. It raises the frequency that the sheet metal will naturally vibrate, so it coincides with typical road noise/exhaust noise frequencies.

[Matt93SE]

That was when my car was still full interior street car. My engine and trans mounts were crap so I replaced them with hockey-puck style mounts. OMFG that was horrible, even with full interior.
I bought a new set of OEM mounts and ran those for several years. When I stripped the interior and caged the car, I no longer cared about noise- I wanted the engine to not move and I wear earplugs on track anyway-- so poly mounts are fine now.

[Russell423]

Are u sure it's exhaust? Mine makes a really brutal noise at that RPM on engine decel, got worse when I replaced subframe bushings. Everything I read points towards driveline harmonics which get worse with aftermarket clutches and or flywheels.