HERCULES sum fit artifact: bump in 1.5 to 0.5 ppm range

The sum fit plot for a HERCULES data collected in midline ACC (20 x 40 x 20 size) is showing an odd artifact in the 1.5 to 0.5 ppm range. Does anyone know by eye what this is / what could cause this (and why it’s in the fit and not the residual)? Or, any recommended resources that review common MRS artifacts that can show up in HERCULES data would be awesome!

None of the artifacts reviewed in the Kreis 2004 review of artifacts look quite like the bump we see here.

Kreis, R. (2004). Issues of spectral quality in clinical1H-magnetic resonance spectroscopy and a gallery of artifacts. NMR in Biomedicine, 17(6), 361–381. doi:10.1002/nbm.891

I’m attaching an image of the fit for the subject with a bump (subject11) as well as an image of what I think is a reasonable fit (subject 3)