Start Low$$ Go Slow
Don't scurry out and buy a new amp, posh cables, etc.
Isolate each wire from your system by detaching each line, first subwoofer, then listen, then right front, listen, left front, then listen, repeat for all lines you may have from your amp.
See if you can establish where your problem is.
Then if you eliminate the noise, then switch out that cable with an alternative that is not causing your predicament. If your noise disappeared, possibly the cable, if not, perhaps your amp.
Could be cables position, though rare. Moving the power cord may help as the other poster listed also.
Do you have a Florescent light fixture near by, this can occasionally cause problems.
If its the amp and you like it, probably needs minor adjustments and cleaning that could run your around $75.00. You can decide if it’s worth the investment. Hope this helps.