Rek'Sai Balance

I don't know if this has been proposed yet, so sorry if I'm just telling you something you already know. I thought of this while looking at the Rek'Sai thread on Reddit.

Her tremor sense is potentially one of her great strengths. I really like the idea on her and don't want the range to be nerfed, but the fact that it's always on does make her life so much easier. So what if it was just an active you could put onto her ultimate while she's burrowed like the rest of her abilities? It weakens her strong early game and forces players to use it more strategically while giving her a weakness that isn't her damage or utility. she doesn't have much at this point so it's clear her strength lies elsewhere in her presence around the map.