Condenser mic...possible failure?

I have a large diaphragm Rode condenser mic that is about 10 Years old. I’ve just discovered on some recent tracking projects that if the gain on the MOTU 896HD is up about 60% or higher I’m and getting a kind of 150hz hash noise in the recording. As a “sound card” the 896hd running fine at all volumes. The vu meter on this input shows a steady bouncing of this odd signal, if I keep the level 50% or less it is much less in output but still very unacceptable.

Is there a classic identifiable sign that the mic is going bad or do I need to search deeper for a different problem?

Thanks in advance

Well to help solve this problem I figured I would post some results. Replaced the potentially bad microphone with a new one. The problem has been solved… the microphone is bad.The only thing I wish is that I knew how to test it and possibly repair it but for now, the case is closed.