"chirping" pickups

[plexibass]

i have a question. last night i subbed for a gig that a friend of mine at the last minute couldnt do. i was unable to use my own basses so i had to use all of his stuff which was already at the gig. he was using an ampeg svt350 and an svt 4x10he classic cab. the first bass i picked up was his DEAN which has active pickups. i, in almost 20 years of playing, have never used a bass with active pickups. this is a 2 part question.

when ever i turned towards the amp/cab there was this "chirping" sound which i have never heard before. really loud and annoying. any ideas? is this because of the active pu? i switched to his '71 fender jazz after 2 songs. passive pu. no more chirping.

question 2 and sorry if this is in the wrong forum. the 4x10he classic cab has a big "dial" on the back that goes from 1-20, i think.numbers worn couldnt make it out. what does this dial do. and what are the extra plugs for? already went to the ampeg site but didnt answe my questions. any help you guys could give would be much appreciated.

 

[Steve]

Hmmm, "Chirping"?

It's hard to say but active basses due to the increased output and high end can be a little more susceptible to all kinds of environmental noise that you won't get from a passive bass. You haven't really been scared until your guitar player sets his cell phone on top of your amp rack and he gets a call in between songs. That will generate a noise like your entire rig is melting down.

The large knob on the back is probably a level control for the tweeter in the cabinet.

The extra plugs are just patch points for adding cabinets or different style cords. Most newer cabinets have (2) 1/4 jacks and (2) speakon jacks on the back plate

 

[The 0x]

The chirping noise is microphonic feedback.