The 5.55 or 223 has a distinctive sound as does the AK and this can cause tactical field problems as to burning a lot of rounds can attract unwelcome visitors. L-Rue
Yeah both weapons make very distinctive sounds.
The .223 cartridge could be termed a 'high impulse' cartridge and since it has a very high velocity you get a combination of the report of the gas escaping the muzzle and the projectile exceeding the speed of sound so you get a very intense report- similar results come from .243 Winchester cartridges- loud SOB.
With the M16/M4/AR-15 you get a high pitched and very hard and sharp report: CRACK!!!
The AK-47 you get a lower pitch sound and a more dull and drawn out Crraacck!
The 5.56 NATO has a much higher gas pressure(62,000 psi to be exact) leaving the barrel at almost 1000 feet per second faster than the 7.62X39 which is much slower, has a lot less gas pressure(only 45,000 psi) and a lower powder charge.
I think the M16/M4 is a little bit louder than the AK-47 for those reasons but their both loud as hell and it would be stupid to fire ether of them both without ear plugs.
Wear ear plugs every time when you shoot with any gun.