That's pretty dang good with a new gun! The loud noise you are hearing is the gun "dieseling". It is burning excess oil. It should stop soon and start to smooth out. I forgot to mention that you should always clean the barrel of a new gun prior to shooting to remove oil in the barrel as well as clean it - sorry about that. Never, ever, use cleaning brushes as you can damage the barrel of the air gun - best to use a bore snake and soft cloth strips with these guns. "Goo Gone" is a great cleaner (Wally world or almost any grocery store will have it) but be sure and pull cleaning strips through the barrel until it is completely dry and clean. Of course, never let any combustionable oil near the piston or seal. Please accept my apology if I am telling you things you already know - just wanted to be sure you and/or your dad get a good start with that new rifle. Looks like you got a good one! BTW, you can also get a trigger mod for that rifle that will get the trigger pull down about as low as anyone might want it.
Cheers