2000 Silverado 5.3L Noisy Fule Pressure Regulator

I recently replaced the fuel pump and afterward started noticing a buzzing/whining sound coming from under the hood. The noise goes away when I remove the vacuum line from the fuel pressure regulator and after the car has been driven for 1/2 to 1 hour. Sometimes it comes back, sometime not, but it always is there at a cold start. Had the shop take a look and they said the fuel pump is ok and recommended replacing the fuel pressure regulator. I did but that but it did not solve it. Any ideas? I suppose I should check the fuel pressure.

Wonder if you have a fuel line against something somewhere and vibration from pump traveling through it making it sound like its under hood?