On an AK47, the muzzle threads are protected by a simple screw-on ring. It's locked by the spring-loaded plunger.
There are 8 indentations on the ring that allows you to tighten it enough so it doesn't rattle. On the AKM, there's only one indentation for the plunger, so the slanted part always wound up in the same location. There is always a bit of wobble and rattle because it never tightens up for that last partial turn. One of the problems with any flash hider in any weapon that needs to index to a certain point. With the M-16A2, with the blank area that's supposed to be on the bottom, shims are used for the final "timing".
The PWS flash hider shown for the AKM has two locking notches, because either side can be on top. They provide the red RTV rubber O-ring to take up the last bit of slack, as you snug it up enough to catch the detent pin, and squeeze the O-ring enough to silence any rattle. RTV rubber ("room temperature vulcanizing") is used in high heat applications (engine valve covers, etc) because it won't melt.
The rest of AKM flash hider's flaws I'm taking the word of various articles I've read. It's basically a rocket nozzle with one side of the exhaust bell sliced off to direct a bigger part of the muzzle blast in an off-axis direction, while trying to provide a bit of muzzle rise by directing the muzzle gases up and to the left. I just knew it had to go because it was loose and rattled by design.
One word of advice: I've found PWS muzzle brakes to be very good, as are some other brands, but all the good stuff, for any weapon, costs around $100. On an indoor range, I've seen the difference on my own rifles between something that will light up the entire firing line, and something that produces just a faint glowing jet that vanishes within a couple of inches of exiting the muzzle device. The faster the muzzle blast can be mixed with cooler air, the smaller the visible signature is, especially in the dark. Even for the AR15s, an efficient flash hider has to be at least twice as long as the factory one, with more vents and swirly passages.
That's important enough for me, for both shooting comfort, and tactical reasons, to invest in a better muzzle device. Getting rid of the annoying rattle is just another bonus.