Recently I decided to upgrade a pair of long in the tooth Shure SE215 IEMs after one too many wonky cables and a disintegrating right ear piece (the drivers are working as well as ever). I settled on the Shure SE535, and even if the 4x price increase hasn’t made my music sound four times better, I’m happy with the purchase.
I was less thrilled to hear a soft hiss when I plugged them into my handy (and affordable) Audioengine D3 DAC/amplifier. Fearing it was a defective product, I sought to have it replaced, but could only get a refund due to a lack of stock. I next ordered the similarly priced Dragonfly Black, and much to my dismay this device exhibited exactly the same issue.
As it turns out, their low impedance (36 Ω) and very high sensitivity (119 dB SPL/mW) make the SE535 IEMs easy to drive and suitable for portable devices with low output at the cost of not meshing so well with amps designed for headphones with higher impedance and lower sensitivity. After doing some more research I ended up with the FiiO K3, which is almost (but not quite) silent with no audio playing, and still within my desired price range. Regrettably Schiit products are overpriced in Australia, so I had to rule them out.
TL;DR: your fancy new IEMs might not be suited to your amp. Do your research before you buy.