Water softener standpipe question

I have a 1 1/2 inch standpipe coming off of a 2 inch drain pipe in my basement. The only thing before the stand pipe is the kitchen sink. And after the standpipe is a pipe coming down from the washing machine. But there is no p trap for the washer, only a running trap a few feet down the line from where the washer drain comes down.

But there is a wye with a service 45 going into a trap and an air gap on top for the water softener. Now the only problem I’m having is I notice some bubbles coming out of the air gap vent. Could it be that the washing machine is draining too fast for that in-line tubing trap to handle?

I have a quick little sketch since I’m having trouble getting a full picture of everything. It seems to work fine when the water softener is backwashing or anything else is draining.

Just wanted a second opinion.