magnepan 3.5. Midrange noise

The midrange driver is a planar magnetic and may have loose wires. These wires are the "voice coil" for this kind of speaker and they can delaminate in some cases. Get a flashlight and examine the driver. The wires often only separate at the edges, so look carefully. The sound that results has a buzzy or "slapping" character. Magnepan will rebuild the speaker at a reasonable cost ($300-400?). They actually strip the diaphragm and reglue the wire. DIY repairs are also possible, although I don't recommend it. Afterward rebuilding, the speaker is more or less new. It is better to do both speakers at the same time because often the drivers in the matching speakers are also delaminating. Good luck!

What sound, or lack of sound are you experiencing?

Check your fuses or just change them, maybe clean all terminals including fuse holder. The MR is usually very robust with the tweeter going before the MR. Switch speakers to make sure the problem is not the amp. Good luck.