Unit makes a loud screechy sound then goes away

Don’t worry this is normal. When these units are brand new you have square brushes riding on round slip rings. The brushes need time to round out and seat properly onto the slip rings. Once seated properly this will happen less frequently. 

Unit makes a low growly sound

It is normal for there to be noise coming from the unit.  There are brushes riding on metal slip rings and a motor spinning at about 2400 rpms.  There is slight noise variation between units.  This is normal. 

In the case there is an abnormal noise issue it is most likely coming from the motor and not the brushes as most commonly believed.  An older motor may make more noise than when it was brand new but may not affect the function of your unit.  If the motor is failing it usually is accompanied by your depth moving or rocking.  If you feel you have an issue you can send the unit in to Vexilar for evaluation.  Motor replacements typically run about $80.00 parts, labor and shipping included.

Unit makes a loud screechy sound continuously

There will be noise coming from these units due the motor running and to the brushes riding on slip rings as the wheel spins.  Typically it takes many years for the average fisherman to wear their brushes out.  If you feel your units noise is not normal send it in to Vexilar for evaluation.  Keep in mind it is normal for there to be slight noise variation between units.

I thought the FLX-28 was silent with the new brushless design? 

The brushless design does make the FLX-28 quieter than other units, however, there still is a motor spinning the light wheel at about 2500rpms.  There is slight noise variation from unit to unit.  This is normal.