Take him to the vet.
Our new connor did a TON of hissing after waking up, I think when he was going pee or poo. I have read that could be a urinary tract infection. I think he hisses less now, anyway. we took him to vet(we really like our vet, father and son vet seem to have experience with gliders) , vet looked him over said he was healthy and had NO signs of infections. didn't want to do a round of antibiotics when he looked so healthy.
So months later connor is doing great, still great weight and active on wheel.
Kirk alone since 2013 and doing great? I don't think it sounds like he has to have a buddy. You know how he usually sounds and acts, if you think its not normal I suggest the vet visit. here it is 45 to 100$