Noise presence at a 433Mhz receiver
The receiver (on the left) is just an RF amplifer followed by a simple demodulator followed by a data slicer or data comparator. They do not recognize data and they do not understand received signal level - they will max-out the RF amplifier until the output signal (noise when there is no potentially valid data transmission being received) is quite high and, when a carrier is present somewhere within the pass-band, its fairly large amplitude will cause the RF gain to drop and the output will take a more conventional shape and look like data.

If you are not transmitting data from its counterpart transmitter then expect purely noise unless of course you remove the antenna and severely limit the ability of noise or a potentially valid transmission to be received.

As for potential interference from your connected equipment yes, this can be a problem - try transmitting data and see what happens to the output.

The next question I guess you might ask is "if there's a bunch of noise outputted when nothing is being transmitted then how can I tell it isn't data?"