I live on the ground floor of a three story condo building.
Occaisionally my toilet starts 'gurguling' and then somtimes the
gurgling is followed by rising water and soap suds.

When this happens, I am not using the plumbing or running water in my
condo at all. Normally, the toilet flushes and the tub drains very
quickly, so I do not think it is a drain clog issue.

My theory is that when one of my upstairs neighbors is doing laundry or
draining their tub, the water falls three stories and hits the bend in
the pipe underneath the my floor causing back pressure. Would an
appropriate fix to this be to add an offset by my ceiling into the
drain pipe to slow the water down?

Any other ideas as to what can be causing this - my theory could be
wrong... And what would some options be to fix this?