Chris answered your question.
To help stop intermod from strong stations the amp likes 12v rather than 5v.
As you have noticed it goes away when using 12v..so may i suggest you use the 12v tee rather than the 5v from your sdr.
This is not a fault with the ccw amp but is down to how the amp works..it is the same with many high end loop amps..they need full working voltage to “ reject” interference from unwanted signals..all my loop amps run at 12v..
Some people can get away with using 5v. Some can not..
Regards Simon g0zen