Phono Cart Impedance Question

I have a little bit of hiss through my 6 ohm, 0.28mV cart but only at a volume pushing the upper end of my listening volume...and it's only audible before I drop the needle, and even then not from the listening position.  I realize I therefore likely have a "non problem"!  

But I still have a generic question on to the sensitivity of producing hiss as it relates to cartridge impedance alone.  If one kept all other cart specs identical (including output of course) would you expect hiss to go up or down at the same volume and system gain if I used an 8 ohm or 12 ohm cart instead?  It seems like the hiss would likely go up just like moving to a higher impedance speaker under the same gain setup but perhaps I'm looking at this incorrectly? I realize moving to a slightly output cart could very well reduce the hiss.

Thoughts?   Sorry if this is a ridiculously obvious question and answer.

By the terms "8 ohm" and "12 ohm", I presume you refer to the internal resistance of the cartridge itself.  Yes?  If so, what is the value of the load resistor in your phono stage.  If the value is anything above 100 ohms, the answer likely would be "no difference".  But it also depends upon what is causing the hiss.  There are a few different sources of noise that might be described as a hiss.  So your question is not very specific.
The hiss from your cart is small compared to phonostage.  One easy way to tell is to listen to hiss with and without cart - I guarantee one will be much greater... 
Also, loading resistor is not important, as it gets shunted by cart during normal operation.  A 47k load is just as quiet as a 100 ohm load once a 10 ohm cart is attached... 

Yes, I was referring to the internal resistance of the cart itself.  I'm running the cart through a SUT set at 30 ohms.  The " white noise"-like hiss is mainly through the tweeter and only becomes audible as volume is increased near the peak of my listening range.  It doesn't change much if I adjust the gain over a 22dB range nor does it change with different loadings.  When I bypass the SUT and use the MC input on my phono stage I still get the same hiss.  I used to have a HOMC (2.0mV) cart and it didn't produce any hiss at all through the same phono stage.  I'm wondering if a ~0.5mV cart would pretty much eliminate the issue.  It just seems to be related to the gain needed on the 0.28mV cart in my system.

Good suggestion.  I disconnected the leads from the cart and I still get the same white noise type hiss.  I have a Herron VTPH-2A.  I'm wondering if it could be a bad tube issue.  I think I'll send Keith a note and see what he thinks.

Other ideas?