Feedback problem

[RhysPlease]

I recently changed the bridge pickup of my SG from a stock 490T to a bareknuckle nailbomb.  It was fine until today...

I had the amp turned up pretty loud, and noticed the guitar was feedbacking pretty badly, so i naturally just touched the strings, expecting it to go away. After a few seconds of silence, the feedback returned, even whilst holding the strings!

This feedback was only happening with the bridge pickup, the neck pickup was silent when i tested it. When i rolled back the volume on the bridge, the feedback died away.

My question is, what is causing this feedback whilst holding strings? And how can i get rid of it?

Edit: a little more info. I was getting the feedback from a peavey bandit amp, with the gain maxed and volume on around 5. With a few tweaks of the amp, the feedback went away, but something like this happened last week as well, but it went away... Anyway, i just plugged into my marshall dsl401, and it only started to squeel when i cranked the master volume to around 8, with the neck pickup squeeling at 10, which is consideribly more volume than the peavey. Is this normal, or is their something wrong with the peavey amp?

Im hoping its the amp  :(

[Madiac]

I guess it could be that the bridge pickup starts squealing earlier because bridge pups usually have higher output and are closer to the strings.

[RhysPlease]

Should it still do that, even though ive got my hands on the strings?

[LP_LOVER]

The neck pickup is silent because it's lower output and because it's further away from the strings.

Check the height of your Nailbomb bridge pickup...if it's NOT TOO CLOSE to the strings, then you should check your amp and the amount of gain you're using.

Always be sure that you're playing through a grounded socket.

[Will]

I'm not too experienced in this department, but maybe its gone microphonic? I have some Dirtyfingers that did that