S-40A carrier every 5 khz

[WA6BHX]

I just acquired an S-40A receiver and it seems to work ok except for a carrier about every 5 khz. What may be causing this and how might I eliminate it? Thank you.

[AC5UP]

It's possible for a marker (calibration) generator to do that, but not likely... Usually they're designed for 100 KC increments and some had a switch for 25 KC resolution, but 5 KC's ? Neverheardofit.

I'm trying to imagine why anyone would want that, or how it could happen by accident. Coming up empty on both concepts.