We put in a new water heater (electric), then realized the water pressure coming into the house was too great and replaced the regulator, setting the pressure at 50lb. Now, the faucets are not powerful, but acceptable, and the toilet fills very slowly but quietly which is nice. However, the pipes have started "singing" intermittently and unpredictably. Any ideas?

When that happens I always check the toilets first. There are a few things that would cause this problem. First make sure the lever is free and not hanging up letting water seep past the flapper. Then check the linkage between the flapper and the flush lever, When the tank is full you should have at least 1/4" of play. I have found this vibration occurs when a very small amount of water is seeping past the flapper causing the ballcock to open just far enough to cause vibration between tha ballcock washer and the seat causing the pipes to pick it up and amplify it. This noise will stop when you jiggle the handle thus seating the flapper firmly. You might also check the edge of your flapper. If it has wavey edges, replace it. Hope this answers your question. If not click on back and we'll explore farther. Regards, Tom