A good check of the health of the receiver system is a System Temperature (Tsys) check. This can be run from the Operator Input window with the command

systemp12

Tsys values are reported after about 15 seconds. Expected values are given in the checklist. If they are unusually high, there could be water (condensation) on the feed window or overcast conditions can raise the Tsys. If you suspect a wet feed window, try another Tsys measurement with the antenna tipped to say 20 degrees elevation (but only after the Antenna checks have been made).