Isolating power for an infrared receiver
No, it's probably not the power supply.  

It's not drawn in the block diagram in the datasheet, but the receiver will have AGC (Automatic Gain Control) to cope with big differences in signal amplitude. When no signal is being sent the AGC will just see the input noise and set the gain based on that. So you get digital noise out. I've seen it often with Vishay receivers: a continuous stream of random pulses, but when a code is sent it's received perfectly. The decoding software shouldn't have problems filtering the noise out, as it will have a much higher frequency than the signal.  

A decoupling capacitor of about 4.7 &micro;F with a 47 &Omega; series resistor on the power supply is recommended, but won't avoid the noise.