Horrible scary sound - what happened?

Impossible to say for sure. Clearly a loose or poor connection somewhere. A common source for this problem is the effects loop, if your amp has one. The jacks(send/return) have little switches built into them that can act up in time. Try cleaning those, or just insert (and leave)a short patch cable into the send/return jacks. If that doesn't fix it, it's off to the repair shop.

 

The effects loop jack switches may be oxidized (a common problem if the amp's effects loop isn't used much).

Try plugging a guitar (or patch) cable into the effects send and return jacks.

 

^
This.

 

Update?..

 

It would have been helpful for a diagnosis if you had mentioned what amp you were using.

 

We don't know those things yet.

As Paul has mentioned knowing the make and model number of your amp would be helpful...

 

Have you been able to reproduce the noise and try patching both effects loops?

A bad solder connection or pot could be the culprit too, but on a premium grade amp like the one you have oxidized effects loop jack switches are a more likely suspect.

 

Sound more like your bass than amp. Had that happen to me and turn out to be my battery connector.

 

+1
The audio sounds like a bad pot to me.

 

If a cracked solder connection is what's causing the problem, then cold, contracted metal may make for an even more intermittent electrical contact.

Have you contacted the amp's manufacturer for advice? The sounds you've recorded may be indicative of an issue which has cropped up before.

 

brute force is the key for something like this. upon powering your amp on if it seems fine, take your fist and give the top of the amp a good thump, if you get the sound you are speaking of, you have dirty jacks, bad pot or a bad solder connection. the smallest amount of vibration can cause this to happen in an amp. tiny cracks occur and they are fine for minute then they cause the crackling from the slightest of vibration.

i know it may sound like hitting your amp is a bad idea, it is not, because the slightest thump can recreate your problem. i get amps in my shop all the time where the customer tells me their amp is making this or that sound and of course when i get in my shop, it doesnt do it. so, i thump the thing and it shows its face. that way i know i can disassemble the amp and locate the bad connection. good luck man.

 

Michael Manring had the same thing going on at this clinic.

 

I had the same problem with my Mo'Bass. I cured it by not allowing the cable to dangle from the input jack. I now rout my cable up through the rack handle and bring it "over the top" so the plug has no downward pull. No mo' problems.

 

Turn the amp off. Shoot some tuner cleaner into the fx loop jacks, then run a phone plug in and out of each of them a few dozen times.

I have an amp which periodically gets oxidation on the fx loop jacks, and because signal is going through those all the time even if nothing is plugged into them, any sort of dirt or crud can interrupt your signal. Pounding on the top of the amp would sometimes fix it, sometimes not. This is an easy thing to do and might save you a lot of hassle.