I have had my M90 for a few years now, never heard anything strange. It is never really cranked even to 1/2 way and is usually playing streaming internet through the RCA line-in at 'office volume' so I can still talk on the phone/employees.
Friday the M90 sounded fine (and everyday before that). Come Monday I noticed the left VU wasn't moving and no sound from the left speaker. I figured out that the line-in/phono switch wasn't making contact and was cutting out the left channel. Fiddled with it and the left VU started swinging and sound was back.
Strange thing is now the left speaker is making a scratchy noise with the bass notes of anything I play through it. Almost like if the voice coil is f'd up from playing it too loud and might be kind of blown. If I play it louder, you can still faintly hear this scratchy bzzz but it is drowned out more because the music is louder but it is still there.
I thought maybe the switches are not making contact or the headphone jack is dirty. I flipped some switches hoping for a quick fix. Didn't make a change.
Right channel is clear.
I plugged in headphones and the sound clear, no scratchy noise.
Can a speaker just 'blow' from age even if the surrounds are good? If the coil is bad for some reason, is there hope for the speaker to be fixed/used?