Just put in new vanity and vessel sink. Contractor had to reconfigure piping under sink with PVC. Sink came with pop-up stopper and tail piece. Loud water noise right below sink hole of water running through and some as it runs down PVC pipe to p trap. How do I fix it? It's loud and annoying but appears to be related to materials not any venting problems. Not a burgling, bubbling gurgle just trickling sounds.