I just finished installing a new bathroom in my house. From left to right I have the tub, the toilet and then the sink. All three of these fixtures are connected to a new 4" PVC drain with vents for all three fixtures. The original toilet is also installed on this line directely above where the PVC goes into the floor into the cast. My problem is that whenever I flush either toilet I hear a loud gurgelling noise coming from the tub drain. I know PVC pipes are loud but that should just be in the basement where the pipes are right? Any ideas to help ease my frustration?

Gurgelling