Do you have proper gain structure? Your input gain setting might be too low and master volume cranked to compensate the output you want from the amp?
Since you don’t have a signal input meter here is how I would set my gain.
Set master volume low as not to blow out your speaker.
Then adjust your gain till you start to hear the input clip, do it slowly, then back off your gain a little.
Now that your input gain is set properly set master volume to desired volume.
If this fixes it dont feel bad, a lot of people don’t know how to set input gain and make it up on the master by mistake.
Since you don’t have a signal input meter here is how I would set my gain.
Set master volume low as not to blow out your speaker.
Then adjust your gain till you start to hear the input clip, do it slowly, then back off your gain a little.
Now that your input gain is set properly set master volume to desired volume.
If this fixes it dont feel bad, a lot of people don’t know how to set input gain and make it up on the master by mistake.