Apparently there is only a possibility of about 1 in 2 million for them to fail, so not likely that you've got a faulty one.
You can cook them if you run them dry, or if the filter is gummed up with crap. I've seen one make alot of noise in an FTO because there was sort of jelly stuff in the tank that blocked the filter. Don't think it does them much good to wire them up backwards either.
Hope this helps.
