I recently bought a condo. It has two bathrooms, one bathroom with a shower/tub combo and one with a stall shower. After the stall shower is used there is knocking/clicking noise in the wall which is between the two bathrooms. This also happens when the sink is draining in the bathroom with the shower/tub combo or if water is drained quickly from the tub. From what I can tell there is no new plumbing, but there was a new sink/vanity installed in the bathroom with the shower/tub. Also, when the water is turned off in the bathroom with the stall shower, there is gurgling noises in the sinks. Both toilets also don't fully flush. Could this be a problem with how the plumbing is vented?

I wonder if the pipes weren't anchored properly, and if you find the plumbing vent, try unscrewing the cap on top and see if it releases air. I have two in my home; one over by my washer where the access is, and the other is an open pipe for sewage gases to escape. They shouldn't be blocked up, but what your describing sounds like a backed up main.