That sounds like poly wire!
Got it in one, polysol or poly wire does seem to produce a mid spike whereas true plain enamel has a flatter response through the mids.However the Seth Lover humbuckers as 'supposed' to be wound with plain enamel so, assuming that's the case,it's probably the result of machine winding bringing the capacitance up and making them a touch honky.
There are a few 'voices' in the winding world trying to shout down the vaildity/importance of plain enamel claiming it sounds no different to polysol......these people either don't play guitar or need a hearing test!
The proof, as all you guys know for fact, is in the tone. Getting hold of plain enamel(good quality plain enamel too) is getting harder but not impossible.To ensure consistency and quality we're buying in increasing quantity to make sure we've always got a healthy supply.