It would be good to identify what the fault actually is. This is the trouble with subjectivity - I might be able distinguish between noise and distortion, but someone else might well hear noise and think of it as distortion. We're all different
To tell if it's noise or distortion, turn the volume to minimum and press your ear to the speaker. If you can still hear audio, use the ISM function to mute the audio by tuning to a dead part of the FM band. Having done that, can you still hear a noise? It's likely to be a low-frequency rumble rather than a hiss. If present, that rumble will certainly interfere with quiet music - which is why one might well describe it as distortion.
Before changing anything, check the settings of the two presets. It's very simple to do - I gave the values you need in post #15. As part of this, it's worth giving the pre-sets a small shot of switch cleaner and exercising them. This is just something that should be done to any set as it arrives - knowing that the mid-point and quiescent current is correct tells you an awful lot about the health of the amplifier. Note that this was rightly suggested as early as post #2.
If the quiescent current and mid-point voltage settings are correct and the "distortion" persists, then change T1. That cures most cases of noise, but sometimes you have to consider changing T2 (although as I mentioned before, I change both on aesthetic grounds). Very occasionally, resistors can play up, but again, as mentioned before, resistor problems are relatively rare of the A205 amplifier, but much more common on the A209 used in the RP38A.