Monitor 70 Series II Twitters

I have a total of 6 Polk Audio Monitor70 Series II and one by one, my twitters have been going bad! So far I have 5 bad ones and one good one left. There are all located on different areas and connected to different receivers, Pioneer SC-1222-K, Yamaha RX-V775 and Onkyo TX-NR838. I also have 6 Polk Audio Monitor60 Series II as surrounds and one of the twitters went bad a few weeks ago as well. Is there an issue with this units? The drivers are all still working with no issues! Please advise. . .

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