LS Noise Trans?

[MD340]

I just bought a 2001 ls with a v8 auto trans and 64k miles
. It runs good but it has a strange noise at low rpms like rattling or dieseling. It is only when it is in gear. It almost sounds like when the catalytic converter goes bad. No check engine or trans lights on any help would be appreciated

 

[northstar11]

My 00 v8 does the same thing. It sound like a friggin diesel. Is horrible. Mine does it even when its in park, bu its worse when its in gear. I have no idea what the deal is, but I also would like to know