Hi,
I'm getting resonances around 300hz when I record my vocals (male) - sounds almost like a deep whistle. I tried setting up layers of blankets in the back, as seen on pic - it mostly helped on the top (which was also problematic), not so much around 300hz. My device is a focusrite scarlett (1st gen) and mic is Shure SM7B, also mic shield as seen.
Can anyone offer some tips to solve this?
 

that's a typical problem in a small recording room.  I would suspect floor - ceiling reflections causing this, potentially enhanced by an even distance between mic-floor and mic sidewall (according to your pic). With wall distance you could play, but since your room has a really low ceiling, there is not much you could do about it, other than moving upstairs and recording in the living room (which may have better acoustics than this hard walled small basement room)

^ Thanks!
Never thought of that. The room you record in is so important, learning that more and more.
You don't think sound absorbing panels in ceiling would help..?  (the floor has a rug btw)