If you hear radio / TV but not other noises at 49MHz, I'd bet on something like wireless headphones or wireless speakers. A harmonic of the original wide FM signal would be wider bandwidth than regular FM and would sound distorted (over-modulated).
http://www.alibaba.com/showroom/wireless-headphone-%252849-mhz%2529.html
https://www.yumpu.com/ro/document/view/18167308/cew112-49mhz-ms-customer-care