It might help if you recorded the audio (and video coinciding) and linked to it on youtube or elsewhere.
Normally the causes and types of sounds that go away after driving awhile, I would not describe as knocking. Typically sounds that go away are temperature related, things with tight tolerances that make a much higher frequency noise like squealing or vibrating.
Does it make the sound if you rev the engine with it in park? If not then my main suspect would be your driver's side wheel CV axle. By the way when referring to left and right side it is always when looking at the vehicle from the driver's seat so your driver's side wheel is the left wheel.
Anyway the CV axle usually makes a noise people describe as clicking and does usually start out during turning before wearing enough to be heard going straight while accelerating or decelerating. One thing to check there is the grease boots on the CV axle, if they have torn then it may have lost grease and/or left dirt in which has worn it. That is the usual cause but extreme driving or an accident can cause damage too, but usually that noise does not go away after drivingi a few km.
There's nothing else I can think of that would cause noise as you describe, well except for two things you should notice like a half flat tire in very cold weather that has a flat spot until it warms up enough to round out again, or if your lug nuts are a little loose and while driving, the brake rotor heats up and takes the slack out. This would also be unusual to happen in such a particular way to stop happening once you have driven a few km.
If the noise seems to steadily increase with your vehicle speed then it is bound to be a driven component, somewhere between the CV axle, wheel bearing, brake system, or the wheel/tire itself, unless you are mistaken about where the noise is coming from then we could add transmission except it seems the least likely.
The normal way to troubleshoot this is to jack up the entire front end, pull the wheel off the side making noise, and poke and pry at all the suspension parts including turning the steering wheel to the side making the noise and observing whether anything gets looser with free play in it.
I should mention I am not familiar with a Skoda Rapid but from a picture it looks like a typical front wheel drive sedan with a coil over strut suspension?
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