You'll need to jack up the RV to replace the air spring, so I'd do it now, using properly rated jack and jack stand. Then you can get under and see exactly what's leaking. It likely is the air spring because they do give a 'bang' when they pop. A tire can also make a loud bang, but since you report low air pressure, I doubt it's a tire. It could be a flexible air line or even a leveling valve blowing apart, but I'd bet on the spring.
Going under now and spraying the bolts with PB Blaster
, would make it easier to remove and replace the air spring when it comes in the mail.