Strange clicking noise only heard while playing back recorded information on cassettes, etc
I remember this sound from my youth; about once or twice a second.  It is either a tape recorder or player problem.
This can be proved by running the machine elsewhere - the clicking will happen wherever the machine is, so proving the smart meter is not the problem.
A forum about tape deck problems is shown below.
I hope you find a solution.
As many people no longer value tape players, you may be able to get a better one with a polite request on Freecycle.org
https://www.tapeheads.net/showthread.php?s=623cb949fec3395c575f44fa0bf2564e&amp;t=31268