I noticed the same thing about a week ago, and have been noticing it ever since.
At first, it was just on 11750, now it's on several frequencies and the actual 11780 signal itself is weaker than usual and distorting.
tonight I also had a Radiobras distortion / spur on 11650. Also 11715....
It happens on all my radios, so I know it's not the radios.
Obviously, their transmitter is in need of some repair.
Re: WEWN on 11870, Radio Catolica -- they've had a whine on their signal for the past two years. Do you hear it also?