Cutting to the chase: When I'm holding it as if I were gonna play it there's a good amount of feedback. If I lay it flat there's no to minimal feedback. What would cause this?

More details + story:
Okay, to start this off, I know feedback can be because of plenty of things.
I know it's my bass, not my cord/amp cause I have another bass, and the feedback is minimal to non-existant with same cord and amp.

So, I have a generic, Playmate Bass (Dean something or another. I bought it two years ago in the ads. First bass.) And I wondered why I stopped playing it.
It has decent tone, and is way more comfortable than my Ibanez. And it even looks better. Then I plugged it in.
There's some horrible feedback. The weirdest part - only when I'm holding it as if I were gonna play it. If I lay it flat, there's no to minimal feedback. What would cause this?
Reminds me of a Metalocalypse episode, Skwisgaar's guitar kept buzzing if he held it, but if his guitar tech held it the buzz would be gone. So he ended recording a solo while skydiving out of a helicopter.
Well, what seemed to be the problem was if his feet were in contact with the ground there would be buzzing. Maybe you could strap yourself with belts and whatnot, attach a rope and fly yourself over the crowd like Gene Simmons.
It's happening - Christmas sweater and all. All I need now is a wireless hook-up or a REALLY long cord.
I just performed at a winter concert with my band last night and that's when I thought of the idea.
Niceee. It'd be so sick to do that, but imagine all the complications. Aha.

But really, why would this happen? O.O
Maybe your amp is not connected to a grounded output. You can look that up on google if you don't know what it is.
Nah, it is. Like I said it works fine with my other bass. Plus, the position of the bass shouldn't affect that.
Is it buzzing or actual feedback?

Buzzing could be a grounding problem.

If its feedback, try to make sure your not facing the amp while you play. Also try turning your basses volume down and your amps volume up (or vice versa).

It could just be that the bass has really hot pick ups. You did say it was dean, didnt you? I was always under the impression that they had notoriously hot pick ups
Feedback, at least I think...
But it's not a grounding problem, I know that for sure.

Facing away from amp didn't help.

And turning down the bass volume worked, but not until the bass' volume was completely down and it was all the amp. Aha.

And the pickups would make A LOT of sense. Since I don't get the feedback with the Ibanez.
I'll go with that. Aha.
[After I checked it out...]
Yeah, definately the pick-ups. I [almost] turned of fthe pick-ups and made the bass volume way up and got no feedback.