I owned a G3 for a few years so I hope I can help. First, I don't recall any rattling or noises from my regulator. As far as I know (and remember) it should sound solid. I could not tell you without looking at it. I also remember somewhere along the line, DP upgraded the internals of the G3 reg - it was the regulator piston (***Oringmonkey.com Oring Kits Paintball Marker O Ring Kits***-ACCESSORIES / UPGRADES-• DP Parts / Upgrades-► DP G3-Dangerous Power G3 Regulator Piston (Updated)
). It might be that your reg has been dismantled and reassembled improperly OR it needs this upgrade. Again, there is no way for me to say without seeing the regulator.
Macro line can be tough, so be persistent. Best way that I know to remove is to first push the macroline further into the fitting, then hold down on the collar of the fitting (so, you will be squeezing down in the same direction that you are pressing the macroline), finally, while holding the collar down, pull back on the macroline to remove it. It might take some finagling, but the secret is in the collar of the fitting. If you just pull on the macroline, it won't budge because it's doing it's job.
For the fittings, the reason stock fittings got a bad rap was due to people not pushing the macroline all the way into the fitting. You have 2 options: keep the DP fittings and use new macroline or replace all. If you are really concerned about it, new fittings and macroline isn't that expensive in the long run. If you decide to replace the fittings, you will need access to wrenches or an adjustable spanner and you will need to buy some teflon tape (aka pipe thread tape) from you local hardware store. One roll is plenty - and a good thing to carry in your parts box.
Basically, put a wrench on the macro fitting (you will see the six sided base) and remove by turning to the left. Once the fitting is out (and you will have to remove the regulator fitting to fully disassemble anyhow), clean out the threads on the reg and fitting and then prepare to reassemble. When using teflon tape, I wrap it in the opposite direction in which the fitting turns. In other words, the fitting screws in clockwise, so I wrap the tape counter-clockwise on the threads. 3 to 4 wraps is sufficient, make sure the air hole is unobstructed, and screw the fitting back in by hand. Once seated, use your wrench and screw in the fitting until its tight (but don't over do it, "snug to tight" is all you need). Air up the marker and listen for leaks. If it's from the fitting, give it another short turn clockwise with the wrench and see if stops the leak. If not, move the macroline around and see if that stops the leak. All in all, you'll figure it out and it will be common sense once you get started. Just remember, teflon tape is a one time deal. If for any reason, you back the fitting off (counter-clockwise), the seal is broken and you will have to redo the tape.
Search for "dp g3 regulator" and watch some youtube movies. If you need anything else let me know. Welcome to MCB.