Warwick Wa300 And Profet3.2

Hi, I recently bought a WA300 head mainly as a back up to my ProFet 3.2 and this was largely based on my excellent experiences with the ProFet 3.2. Firstly, the ProFet is powerful, does the tone I like very well and is astonishingly quiet/noise free for a 300watt amplifier. In fact its whisper quiet even with the input and master on full. There's barely a hiss. It's also excellent for studio work as the fan only engages when its used at very high power levels and it never comes on at studio/rehearsals.
Secondly, the WA300 is similar but has some differences. It has the same power output of the ProFet, it does the tone I like also so all good there. However it's very much noisier than the ProFet 3.2 and by a considerable margin. Based on Warwick's mention of low noise class A operation I don't really know whether my WA300 has a fault or if maybe that's just the way it is and its not as quiet as a ProFet 3.2? For example with the input half way, the master starts to introduce a lot of noise anyway past 12 o'clock. By three quarters the noise is very audible and it sounds like a 30 year old amp with bad coupling caps. I have a 1978 Peavey MarkIII combo, still all original and its whisper quiet at idle with the volume full up. My question to any WA300 users is, do you also get noise past half way on the master or is you're WA300 quiet and well behaved?
For info, I've taken a DI out from the pre-amp and I don't hear any noise. I've also plugged directly into power amp via the return jack and the power amp section seems fine and noise free. It's almost like the preamp and power Amp together somehow generate a lot of noise. I used the same bass and cables for both tests as a reference.

thank you.