Huge noise on pin9 from SPI pins?

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hello everyone. i'm developing rather complex project, , found 1 thing i'm curious about.
arduino spi (pins 10,11,12,13) used control spi lcd,sd card , serial dac.
the pin9 used pwm controlling buck dc-dc converter @ 31.5khz.

in idle state (no pwm, no spi transfer active), noise on pwm pin 9 rather low: 30mv.
but when spi transfer started, random noise increases dramatically 300mv.
the vcc still stable, noise levels less 20mv, no ground noise well.

pin 9 connected via 1k series resistor base of npn transistor, , needs sharp edges, can't add smoothing capacitors here.

so i'm curious: can spi transfer @ full speed (pins 10,11,12,13) generate such huge noise of 300mv on neigboring pin 9?

i imagine has lot how wiring laid out.
sck on pin 13 @ full speed 8 mhz, if have high current load on pin lot of power being switched.
do you  have decoupling caps on external devices?
do have grounding scheme?
all affect signals.

what pins using ss lcd, sd card , dac besides pin 10?

also, low signal may 0.9v vcc = 5v , high current load.
see section 29 of datasheet.


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