Recently I had my regulator replaced as the pressure inside my house was very high and due to that my kitchen faucet and one out of 3 toilet flush would make a rattling noise every time they were turned on. One out 3 showers was also leaking 24/7. After the regulator was replaced, the noise went away but the shower still leaks water every time some one takes a shower in the other bathroom or flushed the toilet. The leaky shower is Delta with one handle. What do I need to do to fix the leak from the shower.

If everything else is fine with the new regulator and your pressure is around 40psi I would simply replace the cartridge in the Delta. Shut down your main, open a faucet to blow pressure, remove handle and escutcheon plate. Remove the cartridge. Some just pull out, some have aclip coming in from the side and some have plate with three screws, whatever you have remove it and take the cartridge with you to Lowe's, Home Depot, ACE really any good hardware store.