Reminds me of talking to (or perhaps I should say attempting to communicate) with Casablanca Control in the 1980s. I used to joke that all the controllers there had to come to work with a bucket which they placed over their heads when they went on duty. Very occasionally you would get a clear one - that's because he had forgotten to bring his bucket with him.
It was so bad I decided to file an MOR. The upshot was that the a/c equipment was on frequency (I recall we were on 25 kHz spacing then) but the ground control was slightly off leading to distortion etc.
I have also noticed a reduction in quality in the UK recently. By comparison when you talk to Maastricht or Rhein ATC they seem to be much clearer.