Loss of Pressure

I just picked up my first two kegs and hooked them up to a regulator my dad got for me. It's not new but it looks like I'm good to go. My question is this:

I hooked up the kegs and turned everything on to about 15psi to make sure everything hold pressure. First of all the tank never stopped completely making noise. I could still faintly hear gas moving. Is this normal? And second (OK I guess 2 questions) I then turned the knob off on the tank and the pressure gauge for the tank side slowly went to 0. Doesn't this mean I'v got a leak somewhere? Shouldn't the regulator have held the tank side even if the tank was turned off?

Either way, I can't wait to get some beer in those bad boys!

This was with no liquid in the kegs right? If so, it does sound like you have a leak. Put a little soapy water in each keg, pressurize and shake it. It's probably the lid.

I have the same problem once in a while.
So I wet the big o-ring on the keg lid, and pressurize it more than that (usually if you hit 20-30 psi, it will seal the keg tight enough to stay sealed even when the pressure drops).

worth a try. make 4.5 gals of seltzer for your test run?