fading

Hey guys and gals, HU:Pioneer 880PRS, Comps:JL TR525-CXi, Amp JBL GTO4000 I believe (older amp for sure) When I first power up everything is good but after a bit my FR speaker fades in and out (not completely), and it happens randomly I haven't found any consistency to replicate the problem...

During high-volume playback (meaning with volume at like 37, 38 or 39 out of 50) when I focused on a particular song for troubleshooting this issue (so I'd have a constant thing I could use to measure whether a new step I tried had a positive effect) the outpu of the highs+mids (aka the 4ch amp)...