Toilet Bubbles when taking a shower

We recently moved into our house (less than a week ago) The house is 65 years old but we had all new drains installed under the house and had or Sewer Main flushed a week ago due to a back up in our guest house(clean out has been clear ever since). Today I took a very short shower and the toilet started bubbling; that was when I got out. Is this the vents or could it still be the main
line even though we had it flushed?
Thanks

There is an obstruction down stream of the toilet and shower. Post a description of your layout.

Call the company that ran the drain last week and tell them. See what they say. Did they pull out any roots?

House and plumbing Layout

The bathroom at the top of the drawing drains to the bottom of the drawing where the main is about 10' away from house. The toilet was recently relocated less than 6'-0" away from the existing vent ( I was told 6' was the max). Not sure if that has anything to do with it but...... Thanks. All drains were replaced, toilet shower and lav. We do live in New Mexic though and lots of chronic root in main problems here!