My guess is that the old drum trap was not vented and thus your new trap is not vented or the vent is clogged. Homes of that age, at least in my area, are generally plumbed with galvanized pipe. The insides rust and flake, the flaking can build up over the years to the point that it clogges the vents particularly on smaller pipe I.D. like 1.5".
When you run the water in the other fixtures the DWV system is trying to draw air but can't so it creates a vacuum and sucks the water out of the trap until it gets some air through it and you hear the gurgling.