Bad bad water /dead animal smell as we open under sink cabinet doors, not coming from inside garbage disposal or inside pipes , it's like coming just from interior under sink can not figure it out even had some plumbers tell me everything (garbage disposal, trap and vent looks normal) been there too long to be dead animal, What!

Could be a dead animal under the cabinet flooring. Mobile homes are subject to the problem because they are fairly open underneath. I found a possum family under one.

Hi Hugoagogo

I'm wondering if there is an Air admittance valve (AAV) under the sink (see image)

https://images-na.ssl-images-amazon.com/images/I/71zjzscvXuL._SX466_.jpg (https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwiAqo3jooLdAhXKmOAKHd8SDIwQjRx6BAgBEAU&url=https%3A%2F%2Fwww.amazon.ca%2FOatey-39018-Sure-Vent-plumbing-pressures%2Fdp%2FB000H5SLWM&psig=AOvVaw3CRwnbVBIL_cF1kSAKPywX&ust=1535082677389179)

If you find anything even remotely similar to the picture under the sink then the AAV has failed and needs to be replaced.

Check it out... post back with thoughts.

Mark