I've bought a unused, new MM6501 system and have a problem with it. When I start to play some music containing lower frequencies, both speakers start to produce rattling sound. It happens around 60-80 Hz, and when it plays lower or higher frequencies everything sounds fine.
It sounds rattle even when speakers placed in air. Total lplay time of the speakers is about 2 hours. When I sent my speakers to local Polk Audio service, they checked and said that everything is fine with speakers.
When I push or pull the speakers by my hands there are no any sounds, crackling or any noise out from speakers.
Also I showed the problem to guy who knows much about speakers and he told me that it can be caused by ventilation grills that are on the back of the speakers and it will probably go away after speakers warm up and when diffusor will become softer.
So my questions are:
1. Is it normal that speakers sounds rattly in the beginning or is it defect?
2. If it is normal, then will it go away after some time?
3. Is it necessary to use high-pass filter to cut frequencies lower than 80 Hz or I can use these speakers from 40 Hz? Why specifications says that speakers are able to play frequencies from 40 Hz?
Thank you. Sorry for my english)