I had this a couple of weeks ago on Blackpool Approach 119.950 whilst transiting to the East of the M6 Motorway- Some transmissions were very faint, I mentioned this and the next transmission was readability five. Later the same occurred - again mentioned and next transmission was fine.
This was when Approach was bandboxed with Tower on 118.400. I suspect that ATC was transmitting on the tower frequency, rather that 119.950 and as such the transmitter was less powerful ??