Fair question, and the honest answer is "it depends which noise" — eMTB motors aren't silent boxes and the sound has several distinct sources. Here's where it actually comes from:
1. The gear reduction
This is the big one. Every mid-drive motor uses a gear train (helical, planetary, or a mix) to reduce the high-rpm electric motor down to crank speed. Those gears meshing under load are what you hear as the
whine or
hum when pedalling. The harder the motor works, the louder it gets —
@Jamo noted exactly that on the 2022 Levo: noise rises with load and as the battery drops.
2. The freewheel / one-way clutch
When you stop pedalling and the motor spins down, or when you coast, you hear a
clicking or
ratcheting. That's the internal clutch disengaging the motor from the drivetrain so you're not dragging it.
@Just gan's "scraping in the nano-second after stopping pedalling" on the new Levo is classic spin-down behaviour.
3. Casing resonance
The motor case amplifies internal noise into the frame, which then acts as a soundbox. This is why two bikes with the
same motor can sound different. Mahle's SL 1.2, as
@Zimmerframe pointed out, uses a two-piece aluminium honeycomb casing specifically to damp this. The M2S vs M2 difference
@Rando_12345 flagged is the same story — M2 lacks the damping the M2S got.
4. Things that aren't the motor at all
This catches a lot of people out:
•
Battery rattle in the down tube — hold the battery in place and wiggle-test it
•
Headset bearings —
@emtbeast found these louder than the motor itself on a Gen 4 Levo demo
•
Chain slap —
@Powerslider sorted his Gen 4 with an STFU guide
•
Sintered brake pads singing (per
@TitusDC)
• Loose bottle cages, SWAT covers, GoPro mounts (
@Tubby G's "motor click" turned out to be a camera mount)
5. Above cut-off "zip"
That two-stroke "zzziiip" some riders describe past 15.5 mph is the motor freewheeling at high cadence — internal components spinning with no load.
So before blaming the motor: isolate it. Coast with no pedalling, pedal with no load, wiggle the battery, check the headset. Most "motor noises" posted on here turn out to be something else entirely.
Which bike and which noise are you chasing? Happy to narrow it down.