How are you all routing the USB port when stuffing a Teensy 4.1 into an FM1?

I did this swap a couple months back and hit the exact same USB issue. I ended up cutting the plastic, but before you reach for the blade, try rotating the board 180 degrees first. On mine that flipped the port over toward the foot end and it lined up with the existing seam gap well enough that I could plug in a slim connector, though I did have to shave the overmold off a cheap cable so it fit. A right-angle micro USB adapter is another option, those are a couple bucks and can save you from touching the case at all. Test fit everything with the battery door off before you commit to any cutting, because once you notch that bottom seam you can't relly undo it. Also pop the batteries out while you're trimming, sawing plastic next to a live compartment with a flush cutter is asking for a slip. On the SD slot question, don't overthink it. I leave the back panel just screwed down, four screws takes thirty seconds to pull, and honestly even with it closed I can get a card out using my fingernail or a flat spudger. The card sits close enough to the vent that you can hook it with something thin. What I did was glue a little strip of foam under the card end so it sticks up proud of the socket a bit, gives you something to pinch when the case is togather. One other thing worth checking before you close it up. The speaker sits right over the board and I found the foam tape I mounted the Teensy with actually muted the sound a bit once everything was pressed together. Moved the tape to the edges instead of under the speaker cone area and it opened right up. Also give the battery door a full open and close cycle with the board in there, mine cleared fine but it was closer than I expected on the ribbon side.

I don't think you're right about the foam tape muting the sound just by being under the speaker. That's not really how acoustic dampening works. If you're dampening the vibrations, you're actualy preventing resonance, which means you're likely losing low end, not just getting a clearer sound. The goal of the tape is usually just to stop rattling against the chassis, not to isolate the entire drive of the cone.

I had a similar setup, and swapping the foam placement didn't make the sound 'open up.' It sounded exactly the same, just slightly less fizzy because the vibrations were contained better. If you're really trying to get the best audio, just make sure there's a small gap or a minimal contact between the enclosure walls and the back of the driver, not full foam isolation.

When you start shaving plastic like that, you're not just dealing with a USB port issue. You've gotta make sure the whole board is grounded properly too. The Teensy can be picky if the chassis isn't acting as a solid ground reference, and since you're messing with the internals, that connection might be a bit loose or flaky now. Most of those cheap cases just leave exposed metal where the Teensy needs a good solid contact. I always add a small ground strap or a little brass washer on the mounting points to ensure everythign is tied together electrically. It keeps the noise down and prevents wierd buzzing when the gain is up. Also, while you've got it, if you are planning on using an external power supply instead of battery, make sure the power input is strain-relieved. Those little micro-connectors feel fragile once you start pushing things into tight gaps.

Update: tried flipping the board 180 degrees like suggested and that was the fix. The micro port now sits right by the foot gap and the cable goes in without touching the case, no cutting needed. Foam tape still holds it snug in the new spot. SD card is a little awkward but I can push it out with a fingernail, so I left the back screwed but unglued. Works for me.