Did I Just damage my LS50M?

[Doodski]

A quick update! First, thank you all for your help and guidance and special thanks to @Doodski for introducing the wave generator which helped me track down my issue.

I contacted KEF and and explained the situation, and they sent me a new driver within a week, free of charge, as I was still under warranty period. I'm so impressed with their service! They gave me instruction on how to swap it myself, but I asked them if they can introduce a repair shop to do it for me, and they sent me to their repair shop and they swap the driver at no cost! Amazing service!

I sold KEF for several years and after I studied to become a electronic tech I had a warranty service deal with KEF. KEF was a great company to deal with both in sales and repair service. When I decided to build (quasi?) transmission line speakers I went to KEF and got the drivers and KEF was good enough to sell me a pair of matched tweeters from the 107.2 speakers.... Very good company. I don't think we ever voided a warranty for any customer. The deal was in-warranty they get extra great service even if drivers seemed damaged in some way and after warranty they pay.