Plastic (vinyl) diaper pants are the ultimate for making some degree of noise.
Basically what he has has done is accelerated the ageing of the material. As plastic waterproof diaper (covers) age they become more brittle and thus this crackling produces the noise. The thicker the gauge of plastic (vinyl) the more noise is to be expected. While the noise produced is often heard it is heard only by the wearer. The plastic diaper cover if worn without diapers will be noisy from the onset until body heat quiets things down. More or less the type of clothing worn and the number of diapers worn underneath will tend to muffle noise.
When worn under pants or shorts (onesies and sleepers) the noise is contained in a small space is not amplified much.
With fewer thinner diapers the plastic has more room to express itself. When worn under a short skirt it can magnified much like a downward facing megaphone. But in reality the noise is really only being heard by the wearer under normal circumstances. This noise being covered by the ambient noise all around us.
When worn in a quiet place - think library - this may not be true. Some types of nylon outerwear and corduroy materials will make just as much noticeable noise and unless someone does a closer inspection the wearer of plastic diaper pants is not going to be discovered. There is a wide range of price; quality and longevity of plastic (vinyl) diaper covers on the market today.
Cheap stuff from Asia; some good - some not so good. With care one should expect to get perhaps a few dozen wearings before thinking of retiring/trashing the diaper cover. It is time when the crotch no longer holds back the flood gates. If is just the elastic in the waist band or a seam in the side you can expect to get by for awhile. Bleach; Baby Oil (Mineral oil) and harsh detergents are definite 'No-Nos' as well as high dryer heat and perhaps outdoor drying in the hot sun. Cloth diapers can take this cleaning but the plastic diaper covers can not. Amusing diaper punishment can be administered by wearing just the plastic diaper cover over a diaper or two and a very short 'T' shirt or babydoll/camisole.
The noise while not very loud will be inescapable and the wearer can always be chided in "Keep quiet someone might notice that you are making way too much noise - and wearing diapers"! Even more so if the diaper cover is LOCKED on and the wearer wearing locking mittens and pacifier gag. Thus the wearer is unable to escape the humiliation. This could go on for hours.
The best part is a bathroom break is not necessary since the wear is wearing his own bathroom. And this all started with the simple wearing of a plastic diaper cover. Be careful ! Be very careful of what you wish for - a fantasy is a terrible thing to let go without someone to share the noise !