The thing with radio is that pretty soon ( under a century) of the discovery of radio we went from a signal with simple modulation ( thus easy to detect as not natural)to a very complex set of spread spectrum transmissions, that to the casual observer, without the knowledge of the spreading key, the rate and the other parameters, is just about the same as pure wideband noise.
This was done to increase data rates, so it is not too hard to think of others not doing the same, and the RF energy from them, well attenuated and with some natural multipath doing a good job of making it undecodable, appearing here as just a slightly increased noise over some wide range. The same with our transmissions, they are just slightly above the Rf noise of the sun, at those frequencies that are easiest to get out of the atmosphere and into space.
There are no plans to have a very large radio telescope antenna ( and this would have to be large, to cover the range from 10Hz to 100GHz) made and sent out into a solar orbit, well away from the RF noise from Earth, and to look for RF noise above the background. The existing ones are there to look for deliberate signals, and we are not doing much of that ourselves, just a few tiny beams that were short period.