I have a Epiphone Les Paul Custom with the stock pickups, played into a Roland Cube 60. Now if I roll the bridge pickup volume up to 10 or the tone pot for it up, I get a really weird sort of feedback. It's weird in the way that it doesn't actually feedback until I start playing, and it's incredibly annoying, since I'm left with either a flat tone or an annoying noise.

What's going on with my rig? I'm plugged directly in, no pedals or anything. It also tends to happen using the hi-gain models such as the Rectifier model, with the gain past mid-way, and if I have my treble at and past 2 o clock.

Sounds like too much treble and gain mixed. Have you tried turning down the gain or treble?
I don't give a shit if you listen to me or not
Yes I do those things, but I never turn my treble on the amp up past 6/7 anyway, and I only turn up the gain for Master of Puppets, where I need to be able to cut through since I played lead guitar.

Would changing pickups help? I've looked at Noise gates and they seem pretty pricey for a guy with no job.
That just seems like a pot issue, how about you don't turn the tone and volume up to 10 and just leave it at 9
If it's really that much of a problem to you, then you should probably wax pot your pickups.
I don't give a shit if you listen to me or not
It happens around the 7/8ish area of the pots, I'm not a "OMG TURN IT TO TEN ALL THE WAY" kinda guy, I just said that since if I'm changing settings on my guitar quickly in the middle of a song, I just kinda push them the full way that they'll go.
the signal strength is is just low enough to not give you feedback unless you play, turn it up a bit more and you'll have that constant feedback playing or not
you can actually control the feedback at that level with some practice and use it in your playing
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By muting your strings or facing the amp or doing a bunch of stuff.

Feedback is extra sound waves being pickuped by your pickups because they resonate through the strings.

You can stop it by muting the strings with your hand either on the fretboard or with the pick hand. Just lay your hand across the strings.

Other than that you can change the pitch of the feedback if you can figure out what string its affecting and use a whammy bar.
Yes, but what's weird with the feedback I get is that it seems to be the same pitch. And my Les Paul has no whammy bar so no luck there.