Possible Problem with Eleven Rack Mic Preamp

I've had no problems running an SM 57 with a TritonAudio FET Head directly into the Eleven Rack mic preamp (for at least a couple of years) until recently. However, whatever audio I record now through that chain sounds as if it's being passed through a "telephone" filter, yet there are no plugins instantiated.



I've tried switching out mic cables and microphones, removing the FET Head from the chain, but getting the same results.



I'm wondering if I need a new mic preamp. Has anyone run into a similar problem? If so, how did you address it?



Many thanks for any help you could offer,

Steve