Replacement Driver Help

The noise is probably your voice coil, rubbing the magnet structure, due to the decayed surround. If it’s still making music, the voice coil isn’t destroyed yet. Check with the guys at Madisound, for a replacement. They used to deal in a plethora of OEM overruns. Not certain if they still do. To repair your original driver, Simply Speakers offers kits, specific to the M-1 mids. With a new driver, unless the Thiele-Small parameters are identical, you’ll change the sound of the system(sometimes radically). An 8 Ohm driver would alter the crossover frequencies, at both ends of it’s assigned range. https://www.simplyspeakers.com/mirage-speaker-repair-foam-edge-kits.html and https://www.madisoundspeakerstore.com/ Here’s a possibility, if yours is the 5DR52015: https://reconingspeakers.com/product/jbl-363686-001-control-1-pro-5-midrangewoofer/ If they were mine, I’d replace the surrounds myself. Of course, I was in the reconing business for years. You might have the Speaker Exchange, replace the surrounds on both your original mids, if you’re not feeling confident.  I wouldn't have them reconed completely, as that would also change those aforementioned T/S parameters.

Awesome, thanks for all that info.  Mine are labeled as 4DR51690. I will give the surround repair a try first. Was not aware that even minor degradation could impact the sound so dramatically. That said, it is only during certain song sequences that I can hear it.  Thanks for the help.

Your very welcome. I edited my post, apparently while you were typing. I meant to include this, regarding Speaker Exchange's surround repair service: https://reconingspeakers.com/speaker-repair/repair-services/