Hello ,

I've got this resonance issue that's been bugging me ...

I own an ESP KH-602 electric guitar . I keep it in Drop C# and when I play C# in any position a strange resonance effect produces ... like a natural harmonic over the note...It's annoying because it can't be muted and it makes the overall sound very messy...I think the springs of the floyd rose or that block of metal holding them together may be vibrating and causing the noise ... what do I do?
How high are the pickups?

If they are high and have a strong magnetic field, they could be "holding" the string.......which is probably not that tight in drop C and acting like a finger lightly touching the string to produce a harmonic.

Do some pinch harmonics around the pickup and see if you hear the same sound only more pronounced.

If so, lower the pickup a bit......it might help.