I ran the Polk 651s for 1.5 years with no problems, but I recently switched over to Infinity 62.11i. Maybe I was just lucky, but I didn't want to push my luck!
Actually my buddy bought his biketronics 7.1 speakers off of EBay and he blew one. And Biketronics replaced it with no problem. They charged him a $50 core charge and he had his new speaker in 3 days. When he sent the bad speaker back he got his $50 back. Biketronics does stand behind their products.
I bought my MM651 speakers legally off of EBay. Now that I got about 4-5 rides in before they blew, Polk says they will not replace them because I bought them off of EBay. If you do not buy their products from one of their authorized dealers, you are SOL. These speakers literally lasted me a week.
THIS right here happened to me word for word for Phillips bluetooth headphones. Seller wasn't an authorized dealer. How the hell are we going to know that? I got my way and got all my money back. they wanted a restocking fee for a broken device. F that. Restock a broken item, I think not Ebay ********.
I've read many examples of the MM series failing but am a bit surprised reading about the DB/DXi failures I've been fortunate with my internet purchases but just paid a bit more today ($160) to buy my RF PBR300x2 from a local authorized dealer.
When i was considering the Polks I contacted them twice, no response. All I wanted to know was if they had identified a problem and solved it. I wonder if it is just in motorcycle applications.
You could try and buy a new set from Polk themselves and then return them the defective ones and tell them those are the ones they sold you. If that works you will have a spare set of speakers.
I thought of doing that (the old switcheroo) but luckily for me the EBay store I bought them from made an exception and decided to help me out and exchange them even though it was outside of their 30 warranty. If you buy off of EBay, look for a company called WEBDEALIN. They are great. They really didn't have to help me out but they did. That's customers service...