The fact that one speaker does it and the other, supposedly identical speaker, means there is a difference in construction between them. However - all affordable speakers are compromised, and even the less affordable ones are still compromised. Choice and quality of material and construction are all decided by accountants, not by the ultimate desirable technical solutions. If you made speaker cabinets out of something very dense and heavy they would perform wonderfully, but they would be super expensive and the freight would be excessive, and people would complain about the weight. So you are going to get lightweight cabs made from plywood or MDF, and they are going to rattle. Sorry, it happens.
Any monitor speaker is a less-than-perfect window giving you a view of the sonic landscape you are creating. Any monitor and room combination is going to be different, so stop thinking that somehow you are going to get yourself the perfecting monitoring enviroment: it does not matter. What matters is that you create a mix that will sound good on any number of wildly different speakers that will be used by your target market. So get several different monitoring options - all with flaws in them - and learn each one and focus on the music you are creating, not on any one particular set of monitors.
It's like windows or optical glasses - everything is flawed, but you can learn to look "through" them, not "at" them. Same with audio monitors - you need to listen "through" them, not "to" them.
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