Changing Arduino Zero PWM Frequency

hi:MartinL
this code seen to affect my ADC 3 input.
any idea?

// Output 250kHz PWM on timer TCC0 (6-bit resolution)
void setup()
{
REG_GCLK_GENDIV = GCLK_GENDIV_DIV(1) | // Divide the 48MHz clock source by divisor 1: 48MHz/1=48MHz
GCLK_GENDIV_ID(4); // Select Generic Clock (GCLK) 4
while (GCLK->STATUS.bit.SYNCBUSY); // Wait for synchronization

REG_GCLK_GENCTRL = GCLK_GENCTRL_IDC | // Set the duty cycle to 50/50 HIGH/LOW
GCLK_GENCTRL_GENEN | // Enable GCLK4
GCLK_GENCTRL_SRC_DFLL48M | // Set the 48MHz clock source
GCLK_GENCTRL_ID(4); // Select GCLK4
while (GCLK->STATUS.bit.SYNCBUSY); // Wait for synchronization

// Enable the port multiplexer for the digital pin D7
PORT->Group[g_APinDescription[7].ulPort].PINCFG[g_APinDescription[7].ulPin].bit.PMUXEN = 1;

// Connect the TCC0 timer to digital output D7 - port pins are paired odd PMUO and even PMUXE
// F & E specify the timers: TCC0, TCC1 and TCC2
PORT->Group[g_APinDescription[6].ulPort].PMUX[g_APinDescription[6].ulPin >> 1].reg = PORT_PMUX_PMUXO_F;

// Feed GCLK4 to TCC0 and TCC1
REG_GCLK_CLKCTRL = GCLK_CLKCTRL_CLKEN | // Enable GCLK4 to TCC0 and TCC1
GCLK_CLKCTRL_GEN_GCLK4 | // Select GCLK4
GCLK_CLKCTRL_ID_TCC0_TCC1; // Feed GCLK4 to TCC0 and TCC1
while (GCLK->STATUS.bit.SYNCBUSY); // Wait for synchronization

// Dual slope PWM operation: timers countinuously count up to PER register value then down 0
REG_TCC0_WAVE |= TCC_WAVE_POL(0xF) | // Reverse the output polarity on all TCC0 outputs
TCC_WAVE_WAVEGEN_DSBOTH; // Setup dual slope PWM on TCC0
while (TCC0->SYNCBUSY.bit.WAVE); // Wait for synchronization

// Each timer counts up to a maximum or TOP value set by the PER register,
// this determines the frequency of the PWM operation:
REG_TCC0_PER = 96; // Set the frequency of the PWM on TCC0 to 250kHz
while (TCC0->SYNCBUSY.bit.PER); // Wait for synchronization

// Set the PWM signal to output 50% duty cycle
REG_TCC0_CC3 = 48; // TCC0 CC3 - on D7
while (TCC0->SYNCBUSY.bit.CC3); // Wait for synchronization

// Divide the 48MHz signal by 1 giving 48MHz (20.83ns) TCC0 timer tick and enable the outputs
REG_TCC0_CTRLA |= TCC_CTRLA_PRESCALER_DIV1 | // Divide GCLK4 by 1
TCC_CTRLA_ENABLE; // Enable the TCC0 output
while (TCC0->SYNCBUSY.bit.ENABLE); // Wait for synchronization
}

void loop() { }