Noisy old MOTU 828 mkII with Logic

Hi,

I have an iMac running Mojave 10.14.6. My ancient firewire MOTU works, but there is a ton of static noise when using the MIC inputs 1 & 2 for external MIDI instruments. Waggling the trim dials back and forth seems to trigger the noise and clear it up. Then the noise/heavy static comes back a bit later. It can be heard it in my bounces. I have two questions: 1. is this addressable? 2. Anyone know how I can use the analog inputs on the backside of the 828? This seems like a perfect workaround but Logic doesn't seem to hear those inputs (say, 3&4) when I select them. I can't figure it out. I'd love to not have to buy a new interface. Any thoughts greatly appreciated.