thanx for the query
as you say there isn't any kind of pain or discomfort means the bleeding isn't caused by night gaurd , because some times if the night guard is ill fitted it might poke on the gum to cause bleeding and pain.
i believe you need a thorough dental cleaning , it might be a possibility that you have developed calculus in that area which is causing gum infection
make sure you keep proper oral hygiene
and sterilize your night guard every morning with denture cleansing kit as unclean night guard carries lot of invisible germs and bacteria causing dental infections.
make sure you brush twice daily and at night after brushing take half cup luke warm water add hallf tbs salt to it and rinse well ur moth with it everyday for 10 days.
some time bleeding is cause due to vit. c deficiency (have lot of citrus fruits and leafy vegetables) or due to hormonal
changes in PUBERTY
AND *PREGNANCY(*in women).
visit the dentist
for a check up and cleaning.