noise through an amp usually indicates a preamp or cabling issue.
sound goes...
sound device -> low level output ->cable -> preamp -> driver -> speakers
if you can, replace the cables routing audio from your sound device (record/cd/mp3/computer) through to the amp. this is often the easiest cheapest solution. be sure it's not passing by any power cables. it can pick up noise from them.
if you can remove the audio cable source from the amp all together and still hear the sound, it's being internally generated from the Preamp stage of the amp where the sound is boosted from a low level from your sound source to the middle level before being used to drive the transistors/MOSFETS that drive the high level of the speakers. this usually necessitates a rebuild of the preamp stage. usually it's just capacitors getting out of whack causing it... but it could be literally anything.
sometimes a faulty mute circuit (if there is one) can cause sound to be generated because the amp isn't being killed off when no music is playing.
you need to narrow down where the noise is coming from before you can figure out what to do about fixing it.