Most pads squeal it's just usually at a frequency you can't
hear.

Cures:

Always lightly sand the disk to remove glaze with fine emery
paper before fitting new pad.

Always use CRC Stop Squeak a pink adhesive goo you put on the
back of the pad and on the shims works in 99% of cases.  If it
does not you can:

a) Chamfering the lead edge of the pads (cut of about 4mm at 45
degrees; or
b) Cut a radial groove into the centre of the pad (i.e in the
same direction as a wheel spoke) to within a few mm of the
backing plate.

Some good pads already have the chamfers and grooves.