Recently I changed my water source to tank and realized the pump was running very quiet as compare to plumbed in.
My line pressure is constant at 2 bar, I have a pressure gauge before the machine. Once the pump kicked in, I can see the pressure dropped to 0.5 and the pump was working very hard and loud.
Is that normal? Or my line pressure is not sufficient?
Should I change it to tank to protect the pump?

Sounds like your water flow rate from the mains is insufficient, which will cause "cavitation" (basically the pump is trying to "suck" water from mains rather than push into the coffee puck). Consensus is that it may not be good for the life of the pump...

If you are using filtration, it might be insufficient capacity for the flow rate of the pump. Or you might have a kinked JG tube, or a closed faucet somewhere...

Then it comes to my question why the pump is smoother when using tank?
When using tank it has no pressure to the pump. The pump will "sucks" the water when needed.
Even with my low line pressure after the filteration, it still has minimum 0.5-1 bar of water direct to the pump.

Does the pump make noise when the flow rate is very slow? Or only when filling the boiler? I agree the most likely cause is cavitation due to insufficient incoming flow rate, especially if there's a filter involved. An accumulator will fix the problem (look for a "water heater expansion tank" at any Home Depot/Lowes/plumbing supply store). Do most plumb-in machines require external pressure? and La Marzocco Linea makes horrible rattling noise and similar threads elaborate on this point.

If you want confirmation of the diagnosis, post a video.

The loud noise only when filling the boiler. During brewing the pump runs smoothly.
When I draw the hot water for 2 times, the pump will activate and started to fill the boiler with the rattling sound.
External accumulator? Any pic or reference?

Yep, cavitation for sure. Go to your local big box store and ask for a water heater expansion tank. Or, if you prefer something smaller, get a Shurflo accumulator. Google "RV Accumulator Tank" and it will lead you to plenty of options.


Image courtesy of espressoparts.com

Forgot to mention, I am using 1/4" from my filter and connect to the pump.
As my whole setup is pretty much using the 1/4 and convert to 3/8 when connecting to the machine.
Could it be the problem?

That certainly doesn't help.

If you want to try a test, remove the filter(s) prior to the pump. They're probably responsible for the majority of the flow rate problem. But if you remove the filter(s) and it still cavitates, then the 1/4" line is the culprit (I'm betting against it). If you install an accumulator, it will be right before the espresso machine. With the accumulator in place, the diameter of its feed line is irrelevant at espresso machine flow rates.

Attach with the pics. Even remove the filter, my outlet is still 1/4"

Sounds to me like there may be a problem with your pressure regulator. Perhaps it's not adjusted correctly. Or maybe it's defective. Or maybe it's hooked up backwards.

The regulators I've used require that you adjust the output pressure while the water is running. You can add a tee with an on/off valve so you can run water while adjusting the regulator. This will also let you flush the filters and draw samples for testing. Alternatively, you can run your GS/3 hot water tap or brew cycle to adjust the regulator. If you did the adjustment when the water wasn't running, then the output pressure may not be what you want.

Does your regulator have a built-in gauge, or are you relying on a gauge after the regulator, or are you relying on the GS/3 boiler pressure gauge? It's OK to make the adjustment with a built-in gauge or one that immediately follows the gauge, but I wouldn't use the GS/3 boiler pressure gauge. I think there are factors that affect the reading of that gauge (like the heater and the gicleur) that wouldn't apply to a gauge before the pump.

Do you know the pressure of your water without the regulator? Is it sufficient to get a 2 BAR output from the regulator?