GRRRR... noob here, FR speakers fading in/out... and its not a loose connection

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. It has also happened when just sitting with the car on or off.

When the problem occurs, ill turn the volume up/down with the nob or move the faceplate back and forth and that seems to "fix" the problem but not always. Also sometimes it seem the occurs with the curves of the road, but im not sure if its coincidence or my imagination

A couple things to note: I have done the basic check of all the connections and they're good, I dont run my system anything close to hard either, my HU does have the infamous blown pico fuse and I have NOT fixed that problem just kinda ignored the alt whine. My battery is an optima red top and my volts are consistently at 14V

Sorry for all the writing just wanted to try and answer some ?'s before you asked

It may be your amp, I had a similar issue and as part of my troubleshooting I replaced the amp with another I had and it solved my problem.

ttt

If it's a pretty common occurance in your car... hook up an ipod to the amp w/ RCA cables (bypass the deck) and play music through that.

If it fades in/out... amp

If it doesn't... headunit or RCA connections.