Toilet "bubbles/gurgles" when washing machine drains

[tomanderson312]

I have a toilet that's started bubbling/gurgling when the washing machine drains. Here's the layout:
1. Washing machine is in the basement. It drains into a sump pump that pumps the water up 8' to the main drain line....which goes out to the septic tank.
2. The toilet is up on the main level.
3. The septic tank was pumped about 6 months ago.
4. There are 2 toilets on the main level, but only this one has the problem.

Any suggestions....

 

[Geofd]

its possible that you have a partial stoppage in your main drain you wouldn't hear it from your gravity fixtures unless you ran them long enough to star filling your main not sure the size of your sump but its being pumped against a partial stoppage