What brand of endoscope did you buy? I'm looking at buying one too. With new O2 sensors ready for installation, looking into the cat would be nice. Mine had an oil smoke when I bought it. It's gone after lots of maintenance.

Is the sound continuously the same pitch? Cat rattle should be random and different.

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'06 X5 3.0i - bought @143,123 miles (12/26/20)