We have played with many sets now. In some cases, you can't hear anything rattling. It depends upon camshaft, compression and size. We have them on a 410 with 10:8 compression and a really big cam. They only slightly thump but the noise of the exhaust pinging through the headers is far worse. The way they quiet and eliminate roar and drone is far better then the little bit of noise they make at idle sometimes.
The wire mesh you see silences the closing thump but as they flap violently, the other side may clatter. Again, big cams, big engines, big compression = thump/rattle.
Not all cars work as well but in our case, they are great. On Dad's 480 cu in Pontiac, they did clank a bit but Walker recommends against the big engine, high compression, big cam set ups.
They are truly great mufflers and since they have a sound guarantee, you have nothing to lose but a bit of time and labor trying them. I say give them a shot if your engine fits the requirements.
Tom
