CRX: audio hum

[Ronnie Overby]

i installed a stereo today in 88 si.   bear in mind no RCA cables involved   a hum can be heard over spearkers when the engine is running....the hum's pitch increases as rpm's increase.   my friend tony said..."need a ground loop isolator"   i went to walmart...all they had was RCA GLI's....   what do i  do????   thanks, ronnie