I recently got an ESA E4407B analyzer. From time to time I hear a faint creak or regular ticking from inside the unit. It happens at the end of (but not everyone's) sweep. To hear it more clearly, I changed the sweep time to 1s. I Will be grateful for any idea, what could be the cause, or is it a some sign of a possible failure? The analyzer passes all the internal test and measures as specified.
Many thanks in advance!