Amp hiss through speakers?

Possibilities - 1) Tubes are not 'low noise tubes' and your amp requires low noise tubes; 2) Speakers are too efficient and reveal the noise floor of your amp; 3) A combo of 1 & 2, 4) Hearing a volume control when it rotates (I assume you are talking about the mechanical noise from the amp, not the speakers) is not really rare and doesn't hurt anything, but if the sound is bleeding thru to the speakers and is quite noticible I'd have the amp checked out. Maybe it just needs cleaning.

I'm sure there are other possibilities but these come immediately to mind, the first being the most likely.

I had a similar issue with Jolida hybrid amp, except it was more of a hum. I found out that it can sometimes be caused by the ground pin on the power cord. Apparently, in some cases, this ground pin can cause a ground loop and introduce hum and buzz in your system. The advice I got from the dealer was to either use a 3-prong to 2-prong "cheater" plug or (if you don't already have one) get a power cord that has a removable ground pin. I removed the ground pin, and the hum disappeared completely ... making the system dead quiet. I was always a little nervous that somehow a certain degree of protection was absent. I ended up getting rid of the amp after a short time.