S70 Shudder

My 99 Volvo S70 will start to shudder when braking below 10 MPH. I’ll be coming to a stop and as soon as i go below ~10 MPH the rpms will drop to ~600 and the car will start shuddering. Once stopped the rpm will go up to ~800 and the whole car will sort of humm like a spots car, except it isn’t one. As soon as I accelerate the problem instantaneously goes away. So my question is, any ideas as to what is causing this and do I need to get it looked at soon? I’m asking about the timeline because I’m a college student and not putting that many miles on it. I’d prefer to wait another month when I’ll be headed home when my mechanic (that I trust dearly)can take a look at it.