First the PD150 records digital audio which has to peak at -20db. or -12 at best and with a marching band hitting it at -10 is way overdriving that channel dude.
second if you are feeding the signal from a mixer then it has to be a mic signal, the PD doesn’t have a true line level in it’s a mic input with a pad.
Also, are you sure that you have manual control of the audio, and it’s not on AGC?
Two last comments; try a different mic see if it sounds better
try the -10db switch on the camera it’s on the operator side upper area wher the audio controls are, oh yeh, are you in a mic level input?
good luck
famous moose