I will also have to say that it is probably underexposure.
I've pushed HP5 to 3200 and got some usable results ranging from a bit underexposed to some very satisfying negatives. I used a fast lenses 50-1.4 and 135-2.8 wide open. I could go handheld at about 1-15 for the 50mm and about 1/60 for the 135mm. I was photographing some street theater performers and some of the audience. In most cases the lighting was just the light from the street lights, those were a bit underexposed. But when there were some strong lights or for some indoors shots with average light, the negatives where magnificent.
I low light I use the slowest shutter speed I can go handheld and my lens wide open. Then with a general metering rule (http://www.fredparker.com/ultexp1.ht...ensity%20Chart) I get the ISO I have to push.