is your receiver screened? (to the extent that you can, minus the hole for the photodiode). An IR optical filter appears black usually, not red. You can probably
use a piece of plastic from an old remote control if this is a hobby project, otherwise the filter material is not cheap. Also, are you sure the AC supply signal that the
receiver is picking up is via optical means, or could it be from the supply rails, or do you have long wires off the photodiode?
Btw, there are different wavelengths for IR devices, so for optimum range you'll want to ensure the photodiode is most sensitive to the IR transmitter wavelength.